Sampling method and apparatuses

• US 4,188,583 A
• Filed: 12/23/1977
• Issued: 02/12/1980
• Est. Priority Date: 12/23/1977
• Status: Expired due to Term

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: RCA Corporation (General Electric Company)
• Inventors: McCurdy, Robert J.
• Primary Examiner(s): Safourek, Benedict V.
• Application Number:
  US05/863,904
• Time in Patent Office: 781 Days
• Field of Search: 332/16, 332/18, 331/78, 179/15 BA, 325/30, 325/141, 325/143, 325/163, 178/66 R, 178/66 A, 364/423, 364/717, 364/111, 364/112, 307/239, 307/240, 307/241
• US Class Current: 341/118
• CPC Class Codes: H03M 1/0629 Anti-aliasing
• CPC Class Codes: H03M 1/128 at random intervals, e.g. digital alias free signal processing [DASP]
• CPC Class Codes: H04L 27/122 using digital generation of carrier signals digital function generators G06F1/02, H04L17/10; generating pulses having stepped portions using digital techniques H03K4/026

Abstract

Apparatus and method for sampling analog signals during successive time periods, the sampling signals being essentially aperiodic. The interval between sampling pulses is selected pseudo-randomly. A circuit for producing essentially aperiodic sampling signals gates a periodic signal through a number of delay means, each having a delay time that is a small fraction of each period, the number of delay means being selected by pseudo-random signals. Periodicity of quantization errors is broken up, thereby reducing concomitant unwanted harmonics of the sampling frequency that are introduced when the sampling signals occur at equal time intervals.

Claims

1. A method for sampling a signal during each of a plurality of successive time periods of equal duration comprising the steps of:

generating a plurality of pseudo random pulses of equal duration with successive ones of said pseudo random pulses occurring during successive ones of said successive time periods of equal duration; and

sampling the signal during each of said pseudo random pulses, the period of a pseudo random pulse during which the sampling occurs being known as a sampling interval, each sampling interval occurring at an essentially random time within said time period, whereby harmonics at the time period recurrence frequency are substantially lessened.

2. A method for producing essentially randomly occurring sampling pulses for sampling an analog signal with a single sampling phase occurring during each one of successive and equal time intervals and comprising the steps of:

producing periodic signals with a single periodic signal occurring during each successive time interval;

producing essentially random signals;

delaying said periodic signals a number of incremental delay times to produce said randomly occurring sampling signals with the total of such delay times being insufficient to move said delayed periodic signal out of its designated time interval, said number of delay times being determined by the said essentially random signal occurring during each periodic signal; and

sampling said signal with said delayed periodic signals.

3. The method as claimed in claim 2 wherein said delaying step comprises gating each of said periodic signals through a particular incremental delay if the essentially random signal has one value and by gating said periodic signal around said delay element if said essentially random signal has another value.

4. A circuit for producing essentially randomly-occurring pulses at an output means comprising, in combination:

means for supplying periodic signals;

means for supplying essentially random signals;

a plurality of selectable delay means connectable ad seriatim between the means for supplying periodic signals and said output means for selectively delaying said periodic signals by varying amounts; and

control logic means responsive to said essentially random signals to gate said periodic signals through selected ones of said delay means to said output means.

5. The invention as claimed in claim 4 wherein said control logic means comprises:

a plurality of first gating means, each associated with one of said plurality of delay means and each responsive to said essentially random signals for selectively coupling a periodic signal through the associated delay means when the essentially random signal has one value and bypassing said associated delay means when the essentially random signal is of another value.

6. The invention as claimed in claim 4 wherein said control logic means comprises:

decoding means responsive to said essentially random signals for producing a plurality of gating signals;

a plurality of gating means each responsive to one of said gating signals to gate one of the periodic signals through a different one of said plurality of delay means when the essentially random signal has one value and bypassing said different one of said delay devices when the essentially random signal is of another value; and

means for coupling the said plurality of second gating means to the output means.

7. In a circuit for producing a linear frequency-modulated waveform including means for supplying a carrier signal, bandpass filter means, and means for injecting samples of said carrier signal into said bandpass filter means, said means for injecting including first phase-shifting means responsive to said carrier signals for shifting the phase thereof by predetermined amounts to produce phase-shifted signals and sequencer means including a plurality of first gating means each having an output means for supplying bursts of said phase-shifted signals to said output means in an order predetermined to reproduce a linear frequency modulated waveform when passed through said bandpass filter means, the improvement comprising:

second phase-shifting means receptive of each of said burst of said phase-shifted signals for producing associated sample signals having altered phases;

means for producing random time signals having a fixed average period and a given period variance;

a plurality of second gating means each coupled to receive as an input signal a selected one of said bursts of said phase-shifted signals and said associated sample signals having altered phases and further responsive to said random time signals to couple one of said input signals to said bandpass filter means during each of said random time signals;

each of said second gating means being coupled to a selected one of said input signals and responsive to a selected one of said random time signals to produce an output signal whose phase is the same as the phase of the burst of phase-shifted signal from which said input signal is derived; and

said bandpass filter means being responsive to said output signals to produce a linear frequency modulated waveform.

8. A digital circuit for producing dithered digital phase signals employed in producing a spectrally pure linear frequency-modulated waveform from the pulsed portions of a dithered pulsed carried signal of frequency f_c, and comprising in combination:

means for supplying undithered digital signals representative of the phase of the linear frequency-modulated waveform at periodic intervals;

means for producing a plurality of corrective digital signals each having a value representative of, and corresponding to, the phase shift of one of the pulse portions of said dithered pulsed carrier signal resulting from the dithered pulsing thereof; and

means for applying each of said corrective digital signals to said undithered signals at a time which is coincident with the dithered pulsed portion of the carrier signal producing the corresponding phase shift.

9. The invention as claimed in claim 8 wherein said means for producing said corrective digital signals includes:

means for producing essentially random signals;

accumulator means for accumulating digital values representative of a phase shift of said dithered pulsed carrier signal in response to said essentially random dithered pulsing of said carrier signal; and

gating means for coupling said accumulator means to said means for applying said corrective digital signals to said undithered digital signals in response to said essentially random signals.

10. The invention as claimed in claim 9 wherein said gating means includes:

decoding means responsive to said essential random signals for producing gating signals; and

transmission means responsive to said gating signals for coupling said accumulator means to said means for applying.

11. The invention as claimed in claim 8 wherein said means for applying includes adder means.