Digital demodulator using numerical processor to evaluate period measurements

• US 5,159,281 A
• Filed: 11/20/1991
• Issued: 10/27/1992
• Est. Priority Date: 11/20/1991
• Status: Expired due to Fees

• Current Assignee: NUM Technology Ltd.
• Original Assignee: NSI Partners
• Inventors: Crego, Charles R., Hedstrom, Mark D., Porter, Robert B.
• Primary Examiner(s): Grimm, Siegfried H.
• Application Number:
  US07/794,150
• Time in Patent Office: 342 Days
• Field of Search: 329/300, 329/301, 329/303-305, 329/310-314, 329/321, 329/327, 329/329, 329/335, 329/340-343, 329/345, 455/214, 455/337, 375/80, 375/82, 375/94-96
• US Class Current: 329/312
• CPC Class Codes: H03D 3/04 by counting or integrating cycles of oscillations arrangements for measuring frequencies G01R23/10
• CPC Class Codes: H03K 9/06 of frequency- or rate-modulated pulses

Abstract

A digital demodulator provides efficient demodulation of frequency modulated, pulse-width modulated, and other temporally modulated signals. Without employing an analog-to-digital converter, modulating signal information is extracted from a modulated signal as numerical information. For frequency demodulation, a high gain stage is applied to an incoming FM signal to produce a corresponding sequence of square waves. The period between zero-crossings of the square waves is accurately measured to within one clock pulse using a high-speed clock and at least one counter. Period information is then provided to a numerical processor, wherein it is at least scaled and low-pass filtered to produce a high-quality demodulated signal with a high signal-to-noise ratio.

Claims

1. A digital demodulator for efficient demodulation of temporally modulated signals, the demodulator comprising:

a zero-crossing event detector, responsive to a temporally modulated signal, that serves to detect zero-crossing events of said temporally modulated signal, and thereby provide zero-crossing event information;

a period measurer, connected to said zero-crossing detector, that serves to receive said zero-crossing event information and measure the period between said zero-crossing events, thereby providing a sequence of period measurement values; and

a numerical processor, connected to said period measurer, that serves to convert said sequence of period measurement values into a demodulated signal with a high signal-to-noise ratio.

2. The digital demodulator of claim 1 wherein said numerical processor includes:

a digital data stream generator that receives and converts said sequence of period measurement values into a digital data stream representative of said demodulated signal; and

an digital-to-analog converter that receives said digital data stream and provides said demodulated signal.

3. The digital demodulator of claim 1 wherein said numerical processor converts said sequence of period measurement values into said demodulated signal in real time.

4. The digital demodulator of claim 1 wherein said zero-crossing detector provides zero-crossing event information as a sequence of square waves with zero-crossings commensurate with the zero-crossings of said temporally modulated signal.

5. The digital demodulator of claim of claim 1 wherein said period measurer includes:

a clock;

a counter; and

a clock pulse gate, connected to said clock, said counter, and said zero-crossing detector, that permits clock pulses to propagate from said clock to said counter in response to zero-crossing event information provided by said zero-crossing detector.

6. The digital demodulator of claim 5 further including:

a second clock pulse gate, connected to said clock and said zero-crossing detector; and

a second counter, connected to said second clock pulse gate.

7. A method for demodulating a temporally modulated signal, the method comprising the steps of:

measuring the period between zero-crossings of an intermediate signal of a modulated signal to provide a sequence of period values; and

numerically processing said sequence of period values to provide a demodulated signal.

8. The method of claim 7 wherein the step of numerically processing includes the steps of:

weighting and scaling said sequence of period values to provide a sequence of weighted and scaled values;

filtering said sequence of weighted and scaled values to provide a sequence of filtered values; and

converting said sequence of filtered values into an analog signal.

9. The method of claim 8 further including the step of:

after the step of weighting and scaling, and prior to the step of filtering, averaging the weighted and scaled values within a sliding window to provide a sequence of averaged values to be filtered.

10. The method of claim 9 wherein the sliding window includes two values and is advanced two values at a time.

11. The method of claim 8 further including the step of:

after the step of weighting and scaling, and prior to the step of filtering, executing a Hamming window function upon the sequence of weighted and scaled values to provide a sequence of values to be filtered.

12. The method of claim 8 further including the step of:

after the step of weighting and scaling, and prior to the step of filtering, executing a Von Hann window function upon the sequence of weighted and scaled values to provide a sequence of values to be filtered.

13. The method of claim 8 further including the steps of:

after the step of weighting and scaling, averaging the weighted and scaled values within a sliding window to provide a sequence of averaged values; and

prior to the step of filtering, executing a Hamming window function upon the sequence of weighted and scaled values to provide a sequence of values to be filtered.

14. The method of claim 7 wherein the step of numerically processing includes the steps of:

weighting and scaling said sequence of period values to provide a sequence of weighted and scaled values;

averaging the weighted and scaled values within a sliding window to provide a sequence of window averaged values;

executing a Von Hann window function upon the sequence of window averaged values to provide a sequence of Von Hann values;

filtering said sequence of Von Hann values to provide a sequence of filtered values; and

converting said sequence of filtered values into an analog signal.

15. The method of claim 7 wherein the step of numerically processing includes the steps of:

weighting and scaling said sequence of period values to provide a sequence of weighted and scaled values;

averaging the weighted and scaled values within a sliding window to provide a sequence of window averaged values;

executing a Hamming window function upon the sequence of window averaged values to provide a sequence of Hamming values;

filtering said sequence of Hamming values to provide a sequence of filtered values; and

converting said sequence of filtered values into an analog signal.