Method and apparatus for transmit beamformer

• US 5,675,554 A
• Filed: 07/15/1996
• Issued: 10/07/1997
• Est. Priority Date: 08/05/1994
• Status: Expired due to Term

• Current Assignee: Siemens Medical Solutions USA Incorporated (Siemens AG)
• Original Assignee: Acuson Corporation (Siemens AG)
• Inventors: Gee, Albert, Cole, Christopher R., Liu, Thomas
• Primary Examiner(s): Pihulic, Daniel T.
• Application Number:
  US08/673,410
• Time in Patent Office: 449 Days
• Field of Search: 367/138, 367/103, 367/105, 367/135, 367/11, 367/7, 364/413.25, 342/81, 342/154, 342/158, 128/660.01, 128/660.04, 128/660.05, 128/661.01, 128/661.07, 73/626, 73/625
• US Class Current: 367/138
• CPC Class Codes: G01S 15/8915 using a transducer array
• CPC Class Codes: G01S 15/8979 Combined Doppler and pulse-echo imaging systems
• CPC Class Codes: G01S 15/8988 Colour Doppler imaging
• CPC Class Codes: G01S 7/52019 Details of transmitters
• CPC Class Codes: G01S 7/52026 Extracting wanted echo signals Doppler systems G01S15/50; Doppler short range imaging systems G01S15/8979
• CPC Class Codes: G01S 7/52046 Techniques for image enhancement involving transmitter or receiver image enhancement by image data processing G06T5/00
• CPC Class Codes: G01S 7/52049 using correction of medium-induced phase aberration
• CPC Class Codes: G01S 7/52066 Time-position or time-motion displays
• CPC Class Codes: G01S 7/5209 using multibeam transmission
• CPC Class Codes: G01S 7/52095 using multiline receive beamforming
• CPC Class Codes: G10K 11/341 Circuits therefor
• CPC Class Codes: G10K 11/345 using energy switching from one active element to another

Abstract

A digital transmit beamformer system with multiple beam transmit capability has a plurality of multi-channel transmitters, each channel with a source of sampled, complex-valued initial waveform information representative of the ultimate desired waveform to be applied to one or more corresponding transducer elements for each beam. Each multi-channel transmitter applies beamformation delays and apodization to each channel'"'"'s respective initial waveform information digitally, digitally modulates the information by a carrier frequency, and interpolates the information to the DAC sample rate for conversion to an analog signal and application to the associated transducer element(s). The beamformer transmitters can be programmed per channel and per beam with carrier frequency, delay, apodization and calibration values. For pulsed wave operation, pulse waveform parameters can be specified to the beamformer transmitters on a per firing basis, without degrading the scan frame rate to non-useful diagnostic levels. Waveform parameters can be specified to the transmitters by an external central control system which is responsible for higher level flexibility, such as scan formats, focusing depths and fields of view. The transmit pulse delay specified per-channel to each transmitter is applied in at least two components: a focusing time delay component and a focusing phase component. The carrier frequency can be specified for each transmit beam, to any desired frequency within a substantially continuous predefined range of frequencies, and a beam-interleaved signal processing path permits operation in any of several predefined processing modes, which define different parameter sets in a trade-off among (1) the number of beams produced; (2) per-beam initial waveform sample interval; and (3) transmit frequency.

Claims

1. An ultrasonic transmit beamformer apparatus for use with an array of ultrasonic transducers comprising:

a source of waveform samples adjustable in amplitude for each of said transducers of said array, for use in producing a first ultrasonic beam; and

circuitry coupled to receive said waveform samples and to apply to each of said transducers of said array output waveforms responsive to the waveform samples for each transducer of said array.

2. Apparatus according to claim 1, wherein said source of said initial waveform samples for the transducers comprises a memory for said waveform samples, and wherein said circuitry comprises a transmitter for each of said number of transducers, each of said transmitters having a respective signal path coupled between the memory for the transmitter and the transducer for the transmitter.

3. Apparatus according to claim 2, wherein each i'"'"'th one of said transmitters weights the waveform samples for the transmitter by a respective weight w_i, said weights w_i being specifiable individually to each of said transmitters.

4. The apparatus of claim 3 wherein the weights are apodization values.

5. Apparatus according to claim 2, wherein each of said transmitters modulates by a desired frequency a signal path waveform responsive to the waveform samples for the transmitter, said desired frequencies being specifiable individually to each of said transmitters.

6. Apparatus according to claim 2, wherein each of said transmitters (1) modulates a signal path waveform responsive to the waveform samples of the respective transmitter by a desired frequency specifiable individually by transmitter, (2) applies a weight to a signal path waveform responsive to waveform samples for the transmitter, the weight being specifiable individually by transmitter, and (3) applies a time delay to a signal path waveform responsive to waveform samples for the transmitter, the time delay being specifiable individually by transmitter.

7. Apparatus according to claim 1, further comprising a source of additional waveform samples,

said circuitry being further coupled to receive said additional waveform samples and to superimpose on the waveform applied to each respective one of said transducers a respective additional waveform responsive to said additional waveform samples.

8. A method for producing an ultrasonic waveform, comprising the steps of:

providing to a signal path waveform samples for said ultrasonic waveform; and

applying to an ultrasonic transducer an output waveform responsive to said initial waveform samples, said method further comprising, prior to said step of applying, at least one of;

the step of modulating by a desired frequency samples in said signal path,

the step of upsampling samples in said signal path,

the step of interpolating samples in said signal path,

the step of time delaying by a time delay samples in said signal path,

the step of focus filtering by a filter samples in said signal path, and

the step of phase rotating by a phase samples in said signal path.

9. The method of claim 8 wherein said at least one step comprises the step of focus filtering, and further wherein said samples are focus filtered to achieve a desired signal delay versus frequency response.

10. The method of claim 8 wherein said at least one step comprises the step of focus filtering, and further in which said step of focus filtering includes the step of delay interpolation.

11. A method according to claim 8, wherein said step of applying further comprises the step of converting samples in said signal path from digital to analog form for application to said transducer.

12. A method according to claim 8, comprising said steps of modulating and upsampling, wherein said step of upsampling comprises the steps of:

upsampling samples in said signal path a first time prior to said step of modulating; and

upsampling samples in said signal path a second time, after said step of modulating and prior to said step of applying.

13. A method according to claim 8, wherein said at least one step includes said step of modulating, wherein said step of providing provides a plurality of waveform sample sets, and said step of modulating produces a corresponding plurality of modulated waveform sample sets.

14. A method according to claim 8, further comprising the step of weighting samples in said signal path by an apodization value.

15. A method according to claim 8, for use in producing a plurality of superposed beams, wherein said output waveform applied to said ultrasonic transducer is responsive further to additional waveform samples.

16. A method for producing a first ultrasonic beam comprising the steps of:

writing waveform samples adjustable in amplitude for said first beam to a memory for each respective one of a plurality of ultrasonic transducers; and

applying to each transducer i a respective i'"'"'th output waveform responsive to the waveform samples for said i'"'"'th transducer.

17. A method according to claim 16, wherein the initial waveform samples are different for at least two of said transducers.

18. A method according to claim 16, each i'"'"'th output waveform having an associated time delay τ

_D,i relative to a common start time, further comprising the step of downloading different τ

_D,i for at least two of said transducers.

19. A method according to claim 16, further comprising the steps of:

downloading a weight W_i for each i'"'"'th one of said transducers, at least two of said W_i being different, each i'"'"'th output waveform having an associated weight W_i.

20. A method according to claim 16, each i'"'"'th output waveform being responsive to a carrier frequency F_c,i, further comprising the step of downloading different F_c,i for at least two of said transducers.

21. A method according to claim 16, further for producing a second beam superposed on said first ultrasonic beam, further comprising the steps of:

writing additional waveform samples for said second beam to said memory for each respective one of a number of said transducers, the waveform samples for said second beam for at least one of said transducers being different from the waveform samples for said first beam for the transducer.

22. An ultrasonic transmit beamformer apparatus, comprising:

a first ultrasonic transducer; and

a first signal path which causes said first ultrasonic transducer to produce an ultrasonic waveform having a carrier frequency F_c which is programmable within a substantially continuous range of frequencies.

23. Apparatus according to claim 22, wherein said signal path comprises:

a source of initial waveform samples coupled to said first signal path;

a first modulator in said first signal path which modulates samples in said first signal path by a nominal center frequency F₀ ;

a second modulator having an output in said first signal path, which modulates samples in the first signal path by a vernier frequency F_v, in which F_c =F₀ +F_v ; and

means for applying to said transducer an output waveform responsive to the real part of said output of said second modulator.

24. The apparatus of claim 22 wherein said signal path comprises:

a source of initial waveform samples coupled to said first signal path;

a first modulator having an output in said first signal path which modulates samples in said first signal path by a nominal center frequency F₀ ;

a second modulator in said first signal path which modulates samples in said first signal path by a vernier frequency F_v, in which F_c =F₀ +F_v ; and

means for applying to said transducer an output waveform responsive to a real part of said output of said first modulator.

25. Apparatus according to claim 23, wherein F₀ is programmable to said signal path from among a plurality of digital processing frequencies.

26. Apparatus according to claim 22, further comprising a source of initial waveform samples coupled to said signal path, said initial waveform samples having a sample rate R_E, wherein said signal path comprises:

a modulator which modulates each sample in the signal path using a phase rotation of 2π

(F_c /F₀ -1)n/N radians, where n is a sample number, F₀ =K_u1 R_E /4, K_u1 is a programmable factor, and N=R_E /F₀.

27. Apparatus according to claim 26, wherein K_u1 is programmable to said signal path from among a plurality of available integer factors.

28. Apparatus according to claim 22, wherein said ultrasonic waveform is one of a plurality of ultrasonic waveforms which said signal path causes said transducer to produce at different times, and wherein said carrier frequency F_c is programmable to said signal path within said range of frequencies, differently for each of said waveforms.

29. Apparatus according to claim 26, wherein said first ultrasonic transducer is one of plurality of ultrasonic transducers forming an array,

wherein said first signal path is one of a plurality of signal paths, each j'"'"'th one of said signal paths causing a respective j'"'"'th one of said transducers to produce a respective j'"'"'th ultrasonic waveform having a respective carrier frequency F_cj,

and wherein said carrier frequencies F_cj are programmable to said signal paths differently for different j'"'"'s.

30. Apparatus according to claim 22, wherein said first ultrasonic transducer is one of a plurality of ultrasonic transducers forming an array,

wherein said first signal path is one of a plurality of signal paths, each j'"'"'th one of said signal paths causing a respective j'"'"'th one of said transducers to produce a respective j'"'"'th ultrasonic waveform having a respective carrier frequency F_cj,

and wherein said carrier frequencies F_cj are programmable to said signal paths differently for different j'"'"'s.

31. Apparatus according to claim 30, further comprising a source of initial waveform samples coupled to said first signal path.

32. Apparatus according to claim 22, wherein said ultrasonic waveform is one of a plurality of ultrasonic waveforms which said signal path causes said transducer to produce at different times, and wherein said carrier frequency F_c is programmable to said signal path within said range of frequencies, differently for each of said waveforms.

33. Apparatus according to claim 32, further comprising a source of initial waveform samples coupled to said signal path.

34. An ultrasonic transmit beamformer apparatus for use with a plurality of ultrasonic transducers arranged in an array, comprising:

a source of quantized initial waveform samples of at least two bits;

output waveforms responsive to said source of samples, said output waveforms to be applied to each of said transducers to produce an ultrasonic beam;

a respective signal path coupled between said source and each of said transducers;

means for time delaying in said signal path to apply a time-delay component according to a delay profile across the array, to which each output waveform is responsive in forming said beam.

35. Apparatus according to claim 34, further comprising a means for phase rotation in said signal path to apply a phase component according to a delay profile across the array, to which each output waveform is responsive in forming said beam.

36. Apparatus according to claim 35, further comprising means for weighting in said signal path to apply a weighting according to an apodization profile across the array, to which each output waveform is responsive in forming said beam.

37. Apparatus according to claim 34, further comprising means for weighting in said signal path to apply a weighting according to an apodization profile across the array, to which each output waveform is responsive in forming said beam.

38. Apparatus according to claim 34, wherein said time-delay component comprises first and second sub-components, wherein said first sub-component time delays samples from said source and said second sub-component time delays samples in each of said signal paths.

39. Apparatus according to claim 38, further comprising means for phase rotation in said signal path to apply a phase component, according to a delay profile across the array to which each output waveform is responsive in forming said beam.

40. Apparatus according to claim 39, further comprising means for weighting in said signal path to apply a weighting according to an apodization profile across the array, to which each output waveform is responsive in forming said beam.

41. Apparatus according to claim 38, further comprising means for weighting in said signal path to apply a weighting according to an apodization profile across the array, to which each output waveform is responsive in forming said beam.

42. A method for transmitting an ultrasonic beam from a plurality of ultrasonic transducers arranged in an array, comprising the steps of:

providing quantized initial waveform samples of at least two bits in a signal path for output waveforms to be applied to each of said transducers to produce said ultrasonic beam;

time delaying in said signal path according to a time-delay component of a delay profile across the array for said beam; and

adjusting phase in said signal path according to a phase component of said delay profile across the array for said beam.

43. Apparatus according to claim 42, further comprising means for weighting in said signal path to apply a weighting according to an apodization profile across the array, to which each output waveform is responsive in forming said beam.

44. A method according to claim 42, wherein said time-delay component comprises first and second sub-components, wherein said first sub-component time delays samples from said source and said second sub-component time delays samples in each of said signal paths.

45. Apparatus according to claim 44, further comprising means for phase rotation in said signal path to apply a phase component, according to a delay profile across the array to which each output waveform is responsive in forming said beam.

46. Apparatus according to claim 45, further comprising means for weighting in said signal path to apply a weighting according to an apodization profile across the array, to which each output waveform is responsive in forming said beam.

47. Apparatus according to claim 44, further comprising means for weighting in said signal path to apply a weighting according to an apodization profile across the array, to which each output waveform is responsive in forming said beam.

48. Art ultrasonic transmit apparatus comprising:

a source of initial waveform samples;

an ultrasonic transducer; and

a signal path coupled between said source and said transducer,

wherein said signal path comprises a digital signal path coupled to a digital-to-analog converter (DAC) coupled to an analog signal path, at least a portion of said source of initial waveform samples and said digital signal path, and at least a portion of said DAC, being combined on an integrated circuit.

49. Apparatus according to claim 48, wherein said digital signal path comprises at least one of the following:

an upsampler, an interpolator, a modulator, a time delay element, a focusing filter, and a phase rotation element.

50. Apparatus according to claim 48, wherein said DAC comprises switches and current setting resistors, said switches being integrated on said integrated circuit and said resistors being separate from said integrated circuit.

51. Apparatus according to claim 50, wherein said DAC has a differential output.

52. Apparatus according to claim 51, wherein said digital signal path encodes digital waveform samples coupled to the DAC to include a sign bit and a magnitude component,

wherein said DAC comprises first and second sub-DACs, each having a digital input receiving said magnitude component of said digital waveform samples and each having an analog output, said analog output path receiving said analog outputs from both of said sub-DACs, said first and second sub-DACs each having an enable input coupled to receive said sign bits of said digital waveform samples, said first and second sub-DACs being alternately enabled on opposite polarities of said sign bits.

53. Apparatus according to claim 48, wherein said DAC has a differential output.

54. Apparatus according to claim 53, wherein said digital signal path encodes digital waveform samples to include a sign bit and a magnitude component,

wherein said DAC comprises first and second sub-DACs, each having a digital input receiving said magnitude component of said digital waveform samples and each having an analog output, said analog output path receiving said analog outputs from both of said sub-DACs, said first and second sub-DACs each having an enable input coupled to receive said sign bits of said digital waveform samples, said first and second sub-DACs being alternately enabled on opposite polarities of said sign bits.

55. Apparatus according to claim 48, wherein said digital signal path comprises an encoder providing digital waveform samples to said DAC in response to respective prior samples, said encoder encoding each of said prior samples into a form which includes a sign bit, a high-order plurality of thermometer-coded bits, and a low-order plurality of binary-encoded bits.

56. Apparatus according to claim 55, wherein said DAC has a differential output.

57. Apparatus according to claim 56, wherein said thermometer-coded bits and said binary-encoded bits together comprise a magnitude component of a digital waveform sample,

wherein said DAC comprises first and second sub-DACs, each having a digital input receiving said magnitude component of said digital waveform samples and each having an analog output, said analog output path receiving said analog outputs from both of said sub-DACs, said first and second sub-DACs each having an enable input coupled to receive said sign bits of said digital waveform samples, said first and second sub-DACs being alternately enabled on opposite polarities of said sign bits.

58. Apparatus according to claim 48, wherein said analog signal path comprises at least one of the following:

a DAC output amplifier, a high voltage amplifier, and a transformer.

59. Art ultrasonic transmit apparatus comprising:

a source of initial waveform samples;

an ultrasonic transducer; and

a signal path coupled between said source and said transducer,

wherein said signal path comprises a digital signal path coupled to a DAC coupled to an analog signal path,

and wherein said DAC has a differential output.

60. Apparatus according to claim 59, wherein said digital signal path encodes digital waveform samples to include a sign bit and a magnitude component,

wherein said DAC comprises first and second sub-DACs, each having a digital input receiving said magnitude component of Raid digital waveform samples and each having an analog output, said analog output path receiving said analog outputs from both of said sub-DACs, said first and second sub-DACs each having an enable input coupled to receive said sign bits of said digital waveform samples, said first and second sub-DACs being alternately enabled on opposite polarities of said sign bits.

61. Apparatus according to claim 60, wherein said digital signal path further encodes said digital waveform samples such that the magnitude component includes a high-order plurality of thermometer-coded bits, and a low-order plurality of binary-encoded bits.

62. Apparatus according to claim 59, wherein said digital signal path comprises an encoder providing digital waveform samples to said DAC in response to respective prior samples, said encoder encoding each of said prior samples into a form which includes a sign bit, a high-order plurality of thermometer-coded bits, and a low-order plurality of binary-encoded bits.

63. Apparatus according to claim 59, wherein said digital signal path comprises at least one of the following elements:

an upsampler, an interpolator, a modulator, a time delay element, a focusing filter, and a phase rotation element.

64. Apparatus according to claim 63, wherein said at least one element is adjustable.

65. Apparatus according to claim 59, wherein said analog signal path comprises at least one of the following:

a DAC output amplifier, a high voltage amplifier, and a transformer.

66. A method for producing an ultrasonic transmit beam, in a system including a plurality of ultrasonic transducers arranged in an array, said system further including a transmitter for each of said transducers, each of said transmitters including a source of initial waveform samples and a signal path coupled between the source of initial waveform samples for the transmitter and the transducer for the transmitter, comprising the steps of:

obtaining for each of said transmitters, an error value for a first parameter which the transmitter uses in its signal path;

downloading to each of said transmitters, a calibration value responsive to the error value obtained for the respective transmitter; and

causing each of said transmitters to provide to its transducer a respective output waveform which is responsive to the calibration value downloaded to the respective transmitter.

67. A method according to claim 66, wherein said step of obtaining an error value comprises, for each given one of said transmitters, the steps of:

producing a test output waveform from only said given transmitter;

examining a signal responsive to said test output waveform.

68. A method according to claim 66, wherein said first parameter is a signal phase, wherein said calibration values downloaded to each of said transmitters are phase calibration values, and wherein each of said transmitters adds a calculated phase to samples in the signal path of the transmitter, the calculated phase for each of said transmitters being responsive to the phase calibration value downloaded to the transmitter.

69. A method according to claim 68, further comprising the step of precomputing at least a portion of said calculated phase prior to said step of causing.

70. A method according to claim 66, wherein said first parameter is a time delay, wherein said calibration values downloaded to each of said transmitters are delay calibration values, and wherein each of said transmitters delays samples in the signal path of the transmitter by a respective calculated delay, the calculated delay for each of said transmitters being responsive to the delay calibration value downloaded to the transmitter.

71. A method according to claim 70, further comprising the step of precomputing at least a portion of each of said calculated delays prior to said step of causing.

72. A method according to claim 66, wherein said first parameter is a gain adjustment wherein said calibration values downloaded to each of said transmitters are gain adjustment calibration values, and wherein each of said transmitters weights samples in the signal path of the transmitter by a respective calculated weight, the calculated weight for each of said transmitters being responsive to the gain adjustment calibration value downloaded to the transmitter.

73. A method according to claim 72, further comprising the step of precomputing at least a portion of each of said calculated weights prior to said step of causing.

74. A method according to claim 66, wherein said ultrasonic transmit beam is one of a plurality of ultrasonic transmit beams transmitted in a scan,

wherein said step of obtaining an error value is part of a step of obtaining a plurality of error values for said first parameter for each of said transmitters, each of said error values in said plurality of error values for a given transmitter being obtained for different conditions of the signal path of the given transmitter,

and wherein said step of downloading a calibration value is part of a step of downloading to each of said transmitters a plurality of calibration values each responsive to the error value obtained for the transmitter for a respective different condition of the signal path of the transmitter,

further comprising the steps of, after a first one of said plurality of beams in said scan is transmitted:

placing each of said transmitters in a respective first one of said conditions; and

programming each of said transmitters to use the previously downloaded calibration value for the first condition in producing an output waveform for a next ultrasonic transmit beam in said scan.

75. A method according to claim 74, wherein two of said different conditions for a given transmitter differ in the transducer to which the transmitter is coupled.

76. A method according to claim 74, wherein two of said different conditions for a given transmitter differ in the carrier frequency of the output waveform which the given transducer is to provide to its transducer.

77. A method for producing an ultrasonic transmit beam, in a system including a plurality of ultrasonic transducers arranged in an array, said system further including a transmitter for each of said transducers, each of said transmitters including a source of initial waveform samples and a signal path coupled between the source of initial waveform samples for the transmitter and the transducer for the transmitter, said signal path including a digital signal path coupled to the source of initial waveform samples, a DAC coupled to the digital signal path, and an analog signal path coupled between the DAC and the transducer for the transmitter, comprising the steps of:

obtaining, for each of said transmitters, a characterization of the frequency response of a member of the group consisting of the analog signal path of the transmitter, the transducer for the transmitter, and the analog signal path of the transmitter in combination with the transducer for the transmitter;

downloading to the source of initial waveform samples for each of said transmitters, a respective set of initial waveform samples which are responsive to said characterization obtained for the transmitter; and

causing each of said transmitters to provide to its transducer a respective output waveform which is responsive to the initial waveform samples downloaded to the respective transmitter.

78. A method according to claim 77, wherein said characterization for each of said transmitters is a set of correction impulse response samples for the transmitter, and wherein said waveform samples downloaded to each of said transmitters are responsive to a respective convolution of said set of correction impulse response samples, obtained for the transmitter, with a set of specifiable waveform samples for the transmitter.

79. A method according to claim 77, wherein the initial waveform samples downloaded to each of said transmitters are real values.

80. A method according to claim 79, wherein the initial waveform samples downloaded to each of said transmitters describe a real waveform envelope.

81. A method according to claim 77, wherein the initial waveform samples downloaded to each of said transmitters are complex values.

82. A method according to claim 79, wherein the initial waveform samples downloaded to each of said transmitters describe a complex waveform envelope.

83. The method of claim 79 wherein said initial waveform samples downloaded to each of said transmitters describe baseband waveform values.

84. An ultrasonic transmit beamformer comprising:

a plurality of independent transmitters each having a source of waveform samples coupled to a signal processing path for processing a signal which is representative of at least one beam; and

wherein each of said independent transmitters performs beamforming operations; and

further wherein said independent transmitters are separate from a control that programs each transmitter with different programmable parameters.

85. The beamformer of claim 84, further wherein:

said independent transmitters comprise means for programming by said control for a number of simultaneous beams at least per transmit event.

86. The beamformer of claim 84, further comprising:

means for programming by said control for a modulation frequency associated with each of the beams, each beam independently programmed for a desired frequency, at least per transmit event.

87. The beamformer of claim 84 in which the source of

waveform samples of each of said independent transmitters can be programmed by said control with a different set of waveform samples at least per transmit event.

88. The beamformer of claim 84, further wherein:

each of said independent transmitters can be programmed by said control with focusing delays for each beam at least per transmit event.

89. The beamformer of claim 84, further wherein:

each of said independent transmitters can be programmed by said control with apodization values for each beam at least per transmit event.

90. The beamformer of claim 84, further wherein:

each of said independent transmitters can be programmed by said control with calibration values at least per transmit event.

91. The beamformer of claim 84 in which at least one of said transmitters comprises:

a means for programming a phase offset storage with a phase adjustment at least per transmit event.

92. The beamformer of claim 84, further in which said parameters of the independent transmitters are programmed by said control at rates that support real time adaptive beamformation.

93. The beamformer of claim 84, further wherein

each of said independent transmitters can be programmed by said control for number of simultaneous beams per transmitter.

94. The beamformer of claim 84, further wherein

said independent transmitters can be programmed by said control for a modulation frequency associated with each of the beams, each beam independently programmed for a desired frequency, per transmitter.

95. The beamformer of claim 84 in which the source of

waveform samples of each of said independent transmitters can be programmed by said control with a different set of waveform samples per transmitter.

96. The beamformer of claim 84, further wherein

each of said independent transmitters can be programmed by said control with focusing delays for each beam at least per transmitter.

97. The beamformer of claim 84, further wherein

each of said independent transmitters can be programmed by said control with apodization values for each beam at least per transmitter.

98. The beamformer of claim 84, further wherein

each of said independent transmitters can be programmed by said control with calibration values at least per transmitter.

99. The beamformer of claim 84 in which each of said independent transmitters further comprises

means for programming a phase offset storage by said control with a phase adjustment at least per transmitter.

100. Art ultrasonic transmit beamformer apparatus, comprising:

a source of initial waveform samples for a first output signal;

a digital signal processing path coupled to said source of initial waveform samples;

a DAC coupled to said digital signal processing path;

an output signal path coupled to said DAC; and

an ultrasonic transducer coupled to said output signal path.

101. Apparatus according to claim 100, wherein said source of initial waveform samples comprises a memory containing said initial waveform samples.

102. Apparatus according to claim 100, wherein said source of initial waveform samples comprises:

a memory containing said initial waveform samples and having a data output coupled to said digital signal processing path, said memory further having an address input; and

a counter having an output coupled to said address input of said memory.

103. Apparatus according to claim 102, wherein said source of initial waveform samples further comprises delay means for delaying readout of initial waveform samples from said memory until said counter reaches a predetermined count.

104. Apparatus according to claim 100, wherein said source of initial waveform samples comprises a source of an impulse coupled to said digital signal processing path.

105. Apparatus according to claim 100, wherein said source of initial waveform samples comprises means for computing said initial waveform samples sequentially and providing them sequentially to said digital signal processing path.

106. Apparatus according to claim 100, wherein said digital signal processing path includes a programmable upsampler.

107. Apparatus according to claim 100, wherein said digital signal processing path includes a programmable interpolator.

108. Apparatus according to claim 100, wherein said digital signal processing path includes a programmable modulator.

109. Apparatus according to claim 100, wherein said digital signal processing path includes a programmable time delay element.

110. Apparatus according to claim 100, wherein said digital signal processing path includes a programmable phase rotation element.

111. Apparatus according to claim 100, wherein said digital signal processing path includes a multiplier for programmable apodization.

112. Apparatus according to claim 100, wherein said digital signal processing path includes an encoder which provides to said DAC samples from said digital signal path in encoded form.

113. Apparatus according to claim 100, wherein said digital signal processing path includes a filter.

114. The apparatus of claim 113 wherein said filter is a focusing filter.

115. Apparatus according to claim 100, wherein said digital signal processing path includes means for time delaying samples in said digital signal path by creating interpolated samples which approximate a desired time delay.

116. Apparatus according to claim 100, wherein said source of initial waveform samples comprises one of the group consisting of (I)(a) a memory containing said initial waveform samples, (b) in combination, (1) a memory containing said initial waveform samples and having a data output coupled to said digital signal processing path, said memory further having an address input, and (2) a counter having an output coupled to said address input of said memory, (c) a source of an impulse coupled to a waveshaping filter in said digital signal processing path, and (d) means for computing said initial waveform samples sequentially and providing them sequentially to said digital signal processing path;

and wherein said digital signal processing path includes at least one of the following;

(II)(a) an upsampler, (b) an interpolator, (c) a modulator, (d) a time delay element, (e) a phase rotation element, (f) an apodization multiplier, (g) an encoder which provides to said DAC samples from said digital signal path in encoded form, (h) a filter, and (i) means for time delaying samples in said digital signal path by creating interpolated samples which approximate a desired time delay.

117. Apparatus according to claim 116, wherein said at least one of elements (II) are programmable.

118. An ultrasonic transmit beamformer apparatus, comprising:

a source of initial waveform samples for a first output waveform;

a signal path coupled to said source of initial waveform samples; and

an ultrasonic transducer coupled to said signal path,

wherein said signal path includes at least two of the following;

an upsampler, an interpolator, a modulator, a time delay element, a phase rotation element, a focusing filter, and an apodization weighting element.

119. Apparatus according to claim 118, wherein said at least one element is adjustable.

120. Apparatus according to claim 118, wherein said signal path comprises in sequence:

(a) an element which applies at least one of phase rotation, apodization weighting, and frequency modulation, to samples in said signal path;

(b) a first adjustable interpolator;

(c) an adjustable time delay;

(d) an adjustable modulator; and

(e) a second adjustable interpolator.

121. Apparatus according to claim 118, wherein said signal path comprises in sequence:

(a) an element which applies at least one of phase rotation, apodization weighting, and frequency modulation, to samples in said signal path;

(b) a first adjustable interpolator;

(c) an adjustable time delay; and

(d) a second adjustable interpolator.

122. Apparatus according to claim 118, wherein said signal path comprises in sequence:

(a) an element which applies at least one of phase rotation, apodization weighting, and frequency modulation, to samples in said signal path;

(b) a first adjustable interpolator;

(c) an adjustable modulator; and

(d) a second adjustable interpolator.

123. Apparatus according to claim 118, wherein said signal path comprises in sequence:

(a) an element which applies at least one of phase rotation, apodization weighting, and frequency modulation, to samples in said signal path; and

(b) an interpolator.

124. Apparatus according to claim 118, wherein said signal path comprises in sequence:

(a) a first adjustable interpolator;

(b) an adjustable modulator; and

(c) a second adjustable interpolator.

125. Apparatus according to claim 118, wherein said signal path comprises in sequence:

(a) a first adjustable interpolator;

(b) an adjustable time delay; and

(c) a second adjustable interpolator.

126. Apparatus according to claim 118, wherein said signal path comprises in sequence:

(a) a multiplier which applies at least one of phase rotation, apodization weighting and frequency modulation to samples in said signal path;

(b) a first adjustable interpolator;

(c) an adjustable delay element;

(d) a processing element which performs at least one of modulation, complex-to-real conversion, and multi-waveform summation, to samples in said signal path; and

(e) a second adjustable interpolator.

127. Apparatus according to claim 118, wherein said signal path comprises in sequence:

(a) a multiplier which applies at least one of phase rotation, apodization weighting and frequency modulation to samples in said signal path;

(b) a processing element which applies at least one of interpolation and adjustable delay to samples in said signal path; and

(c) a processing element which performs at least one of modulation, complex-to-real conversion, multi-waveform summation, and interpolation, to samples in said signal path.

128. The apparatus of claim 118 wherein said signal path comprises in sequence:

a first adjustable time delay operating in conjunction with the source of initial waveform samples;

a multiplier which applies at least one of apodization weighting and a calibration gain adjustment;

a first adjustable phase rotator which applies at least one of focusing phase, calibration phase adjustment, phase component of initial waveform samples, modulation by a vernier frequency component of a carrier frequency, and an arbitrary programmable phase offset;

a first adjustable interpolator;

a second adjustable time delay;

an adjustable modulator; and

a second adjustable interpolator.

129. The apparatus of claim 128 in which said first adjustable interpolator comprises an upsampler.

130. The apparatus of claim 129 in which said first adjustable interpolator further comprises a filter.

131. The apparatus of claim 128 in which said adjustable modulator comprises a second phase rotator.

132. The apparatus of claim 131 in which said adjustable modulator further comprises a filter.

133. The apparatus of claim 128 in which said adjustable modulator further comprises a converter to perform complex to real conversion and a summer to sum multibeam waveforms.

134. The apparatus of claim 128 in which said second adjustable interpolator comprises an upsampler.

135. The apparatus of claim 134 in which said second adjustable interpolator further comprises a filter.

136. Apparatus according to claim 118, wherein said signal path comprises:

a digital signal processing path coupled to said source of initial waveform samples;

a DAC coupled to said digital signal processing path; and

an output waveform path coupled between said DAC and said transducer.

137. Apparatus according to claim 136, wherein said digital signal processing path comprises in sequence:

(a) an element which applies at least one of phase rotation, apodization weighting, and frequency modulation, to samples in said digital signal processing path;

(b) a first adjustable interpolator;

(c) an adjustable time delay;

(d) an adjustable modulator; and

(e) a second adjustable interpolator.

138. Apparatus according to claim 136, wherein said digital signal processing path comprises in sequence:

(a) an element which applies at least one of phase rotation, apodization weighting, and frequency modulation, to samples in said digital signal processing path;

(b) a first adjustable interpolator;

(c) an adjustable time delay; and

(d) a second adjustable interpolator.

139. Apparatus according to claim 136, wherein said digital signal processing path comprises in sequence:

(a) an element which applies at least one of phase rotation, apodization weighting, and frequency modulation to samples in said digital signal processing path;

(b) a first adjustable interpolator;

(c) an adjustable modulator; and

(d) a second adjustable interpolator.

140. Apparatus according to claim 136, wherein said digital signal processing path comprises in sequence:

(a) an element which applies at least one of phase rotation, apodization weighting, and frequency modulation, to samples in said digital signal processing path; and

(b) an adjustable interpolator.

141. Apparatus according to claim 136, wherein said digital signal processing path comprises in sequence:

(a) a first adjustable interpolator;

(b) an adjustable modulator; and

(c) a second adjustable interpolator.

142. Apparatus according to claim 136, wherein said digital signal processing path comprises in sequence:

(a) a first adjustable interpolator;

(b) an adjustable time delay; and

(c) a second adjustable interpolator.

143. Apparatus according to claim 136, wherein said digital signal processing path comprises in sequence:

(a) a multiplier which applies at least one of phase rotation, apodization weighting and frequency modulation to samples in said digital signal processing path;

(b) a first adjustable interpolator;

(c) an adjustable delay element;

(d) a processing element which performs at least one of modulation, complex-to-real conversion, and multi-waveform summation to samples in said digital signal processing path; and

(e) a second adjustable interpolator.

144. Apparatus according to claim 136, wherein said digital signal processing path comprises in sequence:

(a) a multiplier which applies at least one of phase rotation, apodization weighting and frequency modulation to samples in said digital signal processing path;

(b) a processing element which applies at least one of interpolation and adjustable delay to samples in said digital signal processing path; and

(c) a processing element which performs at least one of modulation, complex-to-real conversion, multi-waveform summation and interpolation, to samples in said digital signal processing path.

145. An ultrasonic transmit beamformer apparatus, comprising:

a source of initial waveform samples for a first output signal;

a digital signal processing path coupled to said source of initial waveform samples;

a DAC coupled to said digital signal processing path;

an output signal path coupled to said DAC; and

an ultrasonic transducer coupled to said output signal path,

said apparatus further comprising a delay register receiving first and second delay values and a summer for summing said first and second delay values,

wherein said digital signal processing path delays samples in said digital signal processing path by a time delay responsive to said delay value of said summer.

146. Apparatus according to claim 145, wherein said output signal path provides to said transducer a plurality of output waveforms at different times, further comprising means for precomputing said time delay in advance of each of said times.

147. Apparatus according to claim 145, wherein said first and second delay values are scaled delay values for first and second transmit reference focal ranges, respectively, said summation performed by said delay register completing an interpolation for a desired focal range between said first and second reference focal ranges.

148. Art ultrasonic transmit beamformer apparatus, comprising:

a source of initial waveform samples for a first output signal;

a digital signal processing path coupled to said source of initial waveform samples;

a DAC coupled to said digital signal processing path;

an output signal path coupled to said DAC; and

an ultrasonic transducer coupled to said output signal path,

said apparatus further comprising a delay register receiving first and second delay values and a summer for summing said first and second delay values,

wherein said digital signal processing path modifies the phase of samples in said digital signal processing path by a phase rotation amount responsive to a component of said delay value of said summer.

149. Apparatus according to claim 148, wherein said output signal path provides to said transducer a plurality of output waveforms at different times, further comprising means for precomputing said phase rotation amount in advance of each of said times.

150. Apparatus according to claim 148, wherein said digital signal processing path further delays samples in said digital signal processing path by a time delay responsive to a component of said delay value of said summer.

151. Apparatus according to claim 150, wherein said output signal path provides to said transducer a plurality of output waveforms at different times, further comprising means for precomputing said phase rotation amount and said time delay in advance of each of said times.

152. Apparatus according to claim 148, wherein said first and second delay values are scaled delay values for first and second transmit reference focal ranges, respectively, said summation performed by said delay register completing an interpolation for the desired focal range between said first and second reference focal ranges.

153. A method for controlling an ultrasonic beamformer system, comprising the steps of:

communicating a transmit data set from a central control to a transmit beamformer of said system, said transmit beamformer being coupled to an array of ultrasonic transducers, said transmit data set indicating a transmit delay profile across said array which forms a transmit beam; and

exciting said array of ultrasonic transducers to emit said transmit beam.

154. A method according to claim 153 further comprising the step of:

communicating a receive data set from said central control to a receive beamformer of said system, said receive beamformer being coupled to an array of ultrasonic transducers, said receive data set indicating a receive delay profile across said array which forms said receive beam.

155. A method according to claim 154, wherein said receive data set further indicates an apodization profile across said array.

156. A method according to claim 154, wherein said receive data set further indicates a first and a second delay profile for a first and a second reference focal range, and wherein said receive beamformer interpolates for a desired focal range.

157. A method according to claim 154, further comprising, in said central control, the step of calculating both said transmit delay profile and said receive delay profile from a common sparse reference delay profile.

158. An ultrasonic transmit beamformer comprising:

a plurality of independent transmitters each having a source of waveform samples coupled to a signal processing path for processing a signal which is representative of at least one beam; and

wherein each of said independent transmitters performs beamforming operations; and

further wherein each of said transmitters is independently responsive to a control that programs each transmitter with programmable parameters.

159. The beamformer of claim 158 wherein the control comprises:

means for programming a number of simultaneous beams.

160. The beamformer of claim 158 wherein the control comprises:

means for programming a modulation frequency associated with each of the beams, each beam independently programmed for a desired frequency.

161. The beamformer of claim 158 wherein the control comprises:

means for programming a source of waveform samples per transmitter.

162. The beamformer of claim 158 wherein the control comprises:

means for programming focusing delays for each beam.

163. The beamformer of claim 158 wherein the control comprises means for programming apodization values for each beam.

164. The beamformer of claim 158 wherein the control comprises means for programming calibration values.

165. The beamformer of claim 158 wherein the control comprises means for programming a phase offset.

166. The beamformer of claim 158 wherein the control comprises means for programming said parameters at rates that support real time adaptive beamformation.

167. The beamformer of claim 158 wherein the control comprises means for programming each transmitter with programmable parameters at least per transmit event.

168. The beamformer of claim 158 wherein the first transmitter is programmed with at least one parameter that is different than an associated parameter programmed into a second transmitter.

169. The beamformer of claim 160 wherein a modulation frequency for a first beam is different than a modulation frequency for a second beam.

170. In an ultrasonic transmit beamformer having a signal path, the signal path comprising:

a source of waveform samples;

a digital-to-analog converter (DAC) coupled to said source of waveform samples;

an ultrasonic transducer coupled to said DAC; and

an upsampler to increase a sample rate associated with said waveform samples.

171. The invention according to claim 170 further comprising a plurality of simultaneous waveforms superposed to produce a composite waveform which is applied to said ultrasonic transducer.

172. The invention according to claim 171 wherein each of said plurality of simultaneous waveforms has an associated carrier frequency F_c approximately equal to a factor v times a nominal center frequency F₀, and

wherein v is independently specifiable for each one of said plurality of simultaneous waveforms to result in different values of F_c.

173. The invention according to claim 171, further comprising:

a first signal path portion which performs a first processing for said plurality of simultaneous waveforms; and

a summer downstream of said first signal path portion, which superposes said plurality of simultaneous waveforms to form said composite waveform.

174. The invention according to claim 173 wherein said first signal path portion time-multiplexes said first processing among said plurality of simultaneous waveforms.

175. The invention according to claim 173 wherein said first signal path portion time-interleaves said first processing among said plurality of simultaneous waveforms.

176. The invention according to claim 171 wherein said composite waveform is generated in one of a plurality of processing modes, each of said processing modes defined by a parameter set comprising at least (1) a number N_B of said simultaneous waveforms, (2) a nominal center frequency F₀, and (3) a nominal-center-frequency-normalized waveform sample rate R_E /F₀, wherein R_E is a sample rate associated with said waveform samples;

and

wherein said plurality of processing modes reflects different trade-offs among values of N_B, F₀, and R_E /F₀.

177. The invention according to claim 176 wherein said trade-offs among values includes, for a selected value of one of N_B, F₀, and R_E /F₀, increasing one of the remaining values of N_B, F₀, and R_E /F₀ while causing the other remaining value to decrease.

178. The invention according to claim 171 wherein said composite waveform is generated in one of a plurality of processing modes, each of said processing modes defined by a parameter set comprising at least:

a nominal center frequency F₀ ; and

a number NB of said simultaneous waveforms; and

wherein said plurality of processing modes reflects different trade-offs between values of F₀ and N_B.

179. The invention according to claim 178 wherein a first one of said plurality of processing modes has a smaller N_B and a larger F₀ than a second one of said plurality of processing modes.

180. The invention according to claim 171 wherein said composite waveform is generated in one of a plurality of processing modes, each of said processing modes defined by a parameter set comprising at least:

a sample rate R_E associated with said waveform samples; and

a number N_B of said simultaneous waveforms; and

wherein said plurality of processing modes reflects different trade-offs between values of N_B and R_E.

181. The invention of claim 170 wherein said upsampler increases a sample rate R_g associated with said waveform samples by a factor n=4F₀ /R_E, wherein n is an integer no less than 1 and F₀ is a nominal center frequency.

182. The invention of claim 170 wherein said upsampler increases said sample rate associated with said waveform samples to an input sample rate F_s of said DAC.

183. The invention of claim 170 further comprising a filter in conjunction with said upsampler.

184. The invention of claim 170 further comprising:

a first upsampler to increase a sample rate associated with said waveform samples to produce intermediate waveform samples with an associated intermediate sample rate; and

a second upsampler to increase a sample rate associated with said intermediate waveform samples to produce output waveform samples with an associated sample rate of F_s.

185. The invention of claim 170 further comprising an interpolator to increase a sample rate associated with said waveform samples.

186. The invention of claim 185 wherein said interpolator comprises an upsampler.

187. The invention of claim 186 further comprising a filter in conjunction with said upsampler.

188. The invention of claim 170 further comprising:

a first interpolator for upsampling said waveform samples to produce intermediate waveform samples with an associated intermediate sample rate; and

a second interpolator for upsampling said intermediate waveform samples to produce output waveform samples with an associated sample rate of F_s.

189. The invention of claim 170 further comprising a modulator for modulating said waveform samples by a desired frequency.

190. The invention of claim 189 wherein said modulator comprises a phase rotator.

191. The invention of claim 190 further comprising a filter in conjunction with said phase rotator.

192. The invention of claim 170 further comprising:

a first modulator and a second modulator for modulating said waveform samples in said signal path to produce modulated waveform samples associated with a modulated frequency between 0 and 2F₀, wherein F₀ is a nominal center frequency, and

wherein said first modulator is for modulating waveform samples by F₀ ; and

wherein said second modulator is for modulating waveform samples by a vernier frequency ranging between -F₀ and F₀.

193. The invention of claim 170 further comprising a complex multiplier to adjust an amplitude and phase of said waveform sample.

194. The invention of claim 170 further comprising a phase rotation element to adjust a phase of said waveform samples.

195. The invention of claim 194 wherein said phase rotation element is adapted to apply an adjustable phase to at least one waveform sample to produce a phase-adjusted waveform sample.

196. The invention of claim 195 wherein at least a portion of said adjustable phase corresponds to a phase ramp representing a vernier frequency modulation.

197. The invention of claim 195 wherein at least a portion of said adjustable phase corresponds to a calibration phase value responsive to a signal path calibration procedure to produce calibration phase values.

198. The invention of claim 195 wherein at least a portion of said adjustable phase corresponds to a phase component of a magnitude and phase representation of said waveform samples.

199. The invention of claim 195 wherein at least a portion of said adjustable phase corresponds to a programmed phase offset.

200. The invention of claim 195, wherein at least a portion of said adjustable phase represents a focusing time delay.

201. The invention of claim 170 further comprising a time delay element to delay said waveform samples.

202. The invention of claim 170 further comprising:

a first time delay element that applies a coarse time delay to said waveform samples; and

a second time delay element that applies a fine time delay to said waveform samples.

203. The invention of claim 202 further comprising a phase rotation element that applies a phase rotation representative of a residual time delay to said waveform samples.

204. The invention of claim 170 further comprising a focusing filter for adjusting said waveform samples for delay as a function of frequency.

205. The invention of claim 204 wherein said focusing filter comprises a delay interpolator.

206. The invention of claim 170 further comprising a multiplier for adjusting an amplitude of said waveform samples.

207. The invention of claim 206 wherein said multiplier is adapted to apply an adjustable amplitude to at least one waveform sample to produce an amplitude-adjusted waveform sample.

208. The invention of claim 207 wherein at least a portion of said adjustable amplitude corresponds to an apodization value.

209. The invention of claim 207 wherein at least a portion of said adjustable amplitude corresponds to a calibration amplitude value responsive to a signal path calibration procedure to produce calibration amplitude values.

210. The invention of claim 170 further comprising an output waveform which is applied to said ultrasonic transducer, said output waveform having an associated carrier frequency F_c approximately equal to a factor v times a nominal center frequency F₀,

wherein F₀ is specifiable from a plurality of predetermined available fractions of an input sample rate F_s of said DAC.

211. The invention of claim 210, wherein v is specifiable from within a substantially continuous range between 0 and 2.

212. The invention of claim 170 further comprising an output waveform which is applied to said ultrasonic transducer, said output waveform having an associated carrier frequency F_c approximately equal to a factor v times a nominal center frequency F₀,

wherein said composite waveform is generated in one of a plurality of processing modes, each one of said processing modes defined by a parameter set comprising at least:

said nominal center frequency F₀, and

a nominal-center-frequency-normalized waveform sample rate R_E /F₀, wherein R_E is a sample rate associated with said waveform samples; and

wherein said plurality of processing modes reflects different trade-offs between values of F₀ and R_E /F₀.

213. The invention of claim 212 wherein a first one of said plurality of processing modes has a smaller F₀ and a larger R_E /F₀ than a second one of said plurality of processing modes.

214. The invention according to claim 180 wherein a first one of said plurality of processing modes has a smaller N_B and a larger R_E than a second one of said plurality of processing modes.

215. The invention of according to claim 170 wherein a plurality of said signal paths collectively form said ultrasonic transmit beamformer.

216. An ultrasonic transmit beamformer comprising:

a plurality of transmitters;

initial waveform samples in a waveform processing path per transmitter; and

a control processor per transmitter to adjust the processing of said waveform processing path.

217. The invention of according to claim 216 wherein said initial waveform samples are independently specifiable for each one of said waveform processing paths.