Analog-to-digital and digital-to-analog converters and methods of operation
First Claim
1. A method for converting a non-binary digital word to an analog signal comprising the steps of:
- repetitively generating a predetermined set of timing signals in response to clock signals received from an external source;
decoding a received non-binary digital word to serially generate bit value signals having a first value when the received bit is high and a second value when the received bit is low;
generating an initial feedback signal Vp having a predetermined value in response to only the first timing signal in each set of timing signals;
generating a comparison signal Vc in response to said timing signals, a feedback signal Vp, a reference signal VR, and said bit value signals, said comparison signal having a value
space="preserve" listing-type="equation">V.sub.c =(1-k)V.sub.p +kV.sub.r when said bit value signal has said first value, and generating said comparison signal Vc having a value
space="preserve" listing-type="equation">V.sub.c =kV.sub.p when said bit value signal has said second value, wherein k has a predetermined value in the range of 0<
k<
1/2, and VR is a reference signal having a value equal to the full scale value of the analog signal;
storing said comparison signal Vc to generate said feedback signal Vp for use in the generation of the next sequential comparison signal Vc ;
repeating said steps of generating and storing said comparison signal in response to the remaining timing signals in said set of timing signals using the stored feedback signal Vp ; and
outputting said comparison signal Vc in response to the last timing signal in each set of timing signals to generate an analog output signal having a value corresponding to the value of the received non-binary digital word.
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Abstract
A method and apparatus for converting between analog signals and corresponding digital signals that is accurate relative to the actual value of the input signal, and not relative to the upper limit on the analog input signal. The method and apparatus are disclosed in terms of a serial-feed-back A/D converter that performs an A/D conversion through a plurality of cycles equal in number to the number of bits in the digital output word. In each cycle a comparison voltage is tested to determine if the bit output for the cycle is high or low. The comparison voltage is the amplified difference of the comparison voltage for the preceding cycle and another reference signal. The scale factor for the amplification of the difference between the two signals is one value if the bit value for the preceding cycle was high, and another complementary value if the bit value for the preceding cycle is low. The companion method and apparatus for converting a non-binary digital signal into a corresponding analog signal is also disclosed.
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Citations
24 Claims
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1. A method for converting a non-binary digital word to an analog signal comprising the steps of:
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repetitively generating a predetermined set of timing signals in response to clock signals received from an external source; decoding a received non-binary digital word to serially generate bit value signals having a first value when the received bit is high and a second value when the received bit is low; generating an initial feedback signal Vp having a predetermined value in response to only the first timing signal in each set of timing signals; generating a comparison signal Vc in response to said timing signals, a feedback signal Vp, a reference signal VR, and said bit value signals, said comparison signal having a value
space="preserve" listing-type="equation">V.sub.c =(1-k)V.sub.p +kV.sub.rwhen said bit value signal has said first value, and generating said comparison signal Vc having a value
space="preserve" listing-type="equation">V.sub.c =kV.sub.pwhen said bit value signal has said second value, wherein k has a predetermined value in the range of 0<
k<
1/2, and VR is a reference signal having a value equal to the full scale value of the analog signal;storing said comparison signal Vc to generate said feedback signal Vp for use in the generation of the next sequential comparison signal Vc ; repeating said steps of generating and storing said comparison signal in response to the remaining timing signals in said set of timing signals using the stored feedback signal Vp ; and outputting said comparison signal Vc in response to the last timing signal in each set of timing signals to generate an analog output signal having a value corresponding to the value of the received non-binary digital word. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A non-binary digital to analog signal converter comprising:
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timing signal generator means for repetitively generating a set of timing signals in response to clock signals received from an external clock; decoder means for serially generating bit value signals in response to each bit of a received non-binary word, said bit value signal having a first value when the received bit is high and a second value when the received bit is low; means for generating an initial feedback signal Vp having a predetermined value in response to the first timing signal of each set of timing signals; means for generating a comparison signal Vc in response to said timing signals, said feedback signal Vp, a reference signal VR, and said bit value signals, said comparison signal Vc having a first value
space="preserve" listing-type="equation">V.sub.c =(1-k)V.sub.p +kV.sub.Rwhen said bit value signal has said first value and a second value
space="preserve" listing-type="equation">V.sub.c =kV.sub.pwhen said bit value signal has said second value;
wherein k has a predetermined value in the range from o<
k<
1/2, and VR is said reference signal having a value equal to the full scale value of the analog signal;means for temporarily storing the value of said comparison signal Vc to generate a feedback signal Vp in response to said timing signals, said means for temporarily storing further responsive to the next sequential timing signal for outputing said stored feedback signal Vp to said means for generating a comparison signal Vc ; and means for outputting the last generated comparison signal Vc in response to the last timing signal in each set of timing signals; where the value of said last comparison signal generated during each set of timing signals is said analog signal. - View Dependent Claims (13, 18, 19, 20, 21, 22, 23, 24)
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14. The converter of claim 14 wherein said means for generating said comparison signal Vc comprises:
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a unitary gain amplifier having an input and an output connected to said means for temporarily storing said comparison signal Vc and said means for outputting; a first resistance R1 having a predetermined value connected between said means for generating a first feedback signal Vp and the input of said operational amplifier; means for generating said reference signal VR in response to said bit value having said first value; a second resistance R2 connecting said means for generating said reference signal VR to the input of said unity gain amplifier, said second resistance R2 having an ohmic value related to the ohmic value of said first resistance R1 according to the equation
space="preserve" listing-type="equation">R.sub.2 =((1-k)/k)R.sub.1means for generating a ground signal in response to said bit value signals having said second value; a third resistance R3 connected between said means for generating a ground signal and the input of said unity gain amplifier, said third resistance R3 having an ohmic value related to the value of said first resistance R1 by the equation
space="preserve" listing-type="equation">R.sub.3 =(k/(1-k))R.sub.1 - View Dependent Claims (15, 16, 17)
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Specification