UNIVERSAL DEMODULATION SYSTEM

• US 3,614,627 A
• Filed: 10/15/1968
• Issued: 10/19/1971
• Est. Priority Date: 10/15/1968
• Status: Expired due to Term

• Current Assignee: Quanta System, S.p.A. (El.En. S.p.A)
• Original Assignee: Owen J. Ott, Raymond A. Runyan
• Inventors: Runyan, Raymond A., Ott, Owen J.
• Primary Examiner(s): Griffin, Robert L.
• Assistant Examiner(s): Mayer, Albert J.
• Application Number:
  US04/767,628
• Time in Patent Office: 1,099 Days
• Field of Search: 325/344,345,346,442,430-438,452,453,457,472,473,474,477,479,480,481,489 329/154 324/79 327/153
• US Class Current: 455/207
• CPC Class Codes: H03D 3/00 Demodulation of angle-, frequency- or phase- modulated oscillations H03D5/00, H03D9/00, H03D11/00 take precedence
• CPC Class Codes: H04L 5/06 the signals being represented by different frequencies combined with time-division multiplexing H04L5/26

Abstract

An FM demodulation system useful to demodulate any carrier signal of any deviation within prescribed ranges with unitary apparatus. A plurality of band pass filters is employed, each filter having a predetermined bandwidth, and selected filters are operatively arranged with a plurality of frequency translators such that an input signal can be heterodyned to the center frequency of the filter having the requisite bandwidth for the deviation of the particular input signal.

Claims

1. A frequency translation system comprising:

a plurality of frequency translator stages, each stage having a group of n band-pass filters and a mixer adapted to be selectively coupled to said band-pass filters, the center frequency of each stage being related to the center frequency of the adjacent stage by a factor M, the bandwidths of the filters in each group differing by M1/n;

control means coupled to said frequency translator stages for selecting predetermined ones of said stages and for selecting a predetermined one of said filters in each selected stage;

means coupled to said stages for applying an input signal to the selected one of the filters of said first selected stage; and

means for providing a reference signal to said mixers such that the output signal of each mixer is the center frequency of the succeeding stage.

2. A frequency tranSlation system according to claim 1 wherein M and n each equal 2.

3. A frequency translation system according to claim 1 wherein said reference signal applied to each mixer is of a frequency 1 +1/M higher than the center frequency of the respective stages

4. A frequency translation system according to claim 1 wherein said reference signal means includes means for delaying said reference signal by an amount such to maintain predetermined phase coherence between said reference signal and said input signal being processed.

5. A frequency translation system according to claim 1 wherein said reference signal means includes means for providing a reference signal of a master frequency, and means for dividing said master frequency to a frequency 1 +1/M higher than the center frequency of each stage.

6. A demodulation system comprising:

a plurality of frequency translator stages, each stage having a group of n band-pass filters, the center frequency of which is related to the center frequency of the adjacent group of band-pass filters by a factor M, the bandwidths of the filters in each group differing by M1/n;

control means coupled to said frequency translator stages for selecting predetermined ones of said stages and for selecting a predetermined one of said filters in each selected stage;

means coupled to said stages for applying a modulated input signal to the selected filter of the first selected stage;

means in cooperative association with said stages for heterodyning said input signal to the center frequency of the selected filter whose bandwidth corresponds to the deviation of the input signal and for applying said heterodyned signal to said selected filter; and

means coupled to the last selected stage for providing an output signal representative of the data content of said modulated input signal.

7. A demodulation system according to claim 6 wherein said heterodyning means includes:

means for providing a reference signal;

a mixer associated with each pair of adjacent stages, one input to each mixer being a signal from the selected filter of one of said pair of adjacent stages, the other input being said reference signal which is of a frequency such that the mixer output signal is of a frequency equal to the center frequency. of the other of said pair of adjacent stages.

8. A demodulation system according to claim 6 wherein said input signal means includes a programmable input low-pass filter having a selectably cutoff frequency related to the deviation of an input signal.

9. A demodulation system according to claim 6 wherein said output signal means includes a limiter and a phase demodulator.

10. A demodulation system according to claim 6 further including means for selectively inverting the output signal in accordance with the number of stages selected, thereby to provide an output signal of uniform polarity irrespective of the number of states selected.

11. A demodulation system according to claim 10 wherein said selective inverting means is part of said control means.

12. A demodulation system comprising:

a programmable input low-pass filter;

means for applying a modulated input signal to said input filter;

a multistage frequency translator, coupled to said input filter including in each stage a group of band-pass filters and a mixer, means for connecting a selected one of said filters to said mixer, said mixer being operative to provide in response to said input signal, an output signal of a frequency to drive the succeeding stage;

means coupled to said translator for selecting a cascade of stages within said translator, whereby said input signal is directed to processing selected filter whose bandwidth corresponds to the deviation of said input signal; and

means coupled to the last selected stage within said translator for decoding the data content of said modulated input signal after processing By said translator.

13. An FM demodulation system according to claim 6 wherein said output signal means includes:

a limiter coupled to the last selected stage;

a phase lock loop coupled to the output of said limiter and having a phase demodulator, a programmable loop filter, a voltage controlled oscillator and a programmable frequency divider;

control means for causing said frequency divider to provide a frequency equal to the center frequency of the selected filter corresponding to the input signal deviation; and

control means for adjusting the characteristics of said loop filter in accordance with input signal conditions.

14. An FM demodulation system according to claim 13 further including:

a programmable low-pass filter coupled to the output of said phase lock loop and having selectable characteristics corresponding to the input signals conditions;

an inverter coupled to said programmable low-pass filter for selectively inverting said output signal in accordance with the number of stages selected; and

a variable gain amplifier coupled to said inverter and operative to provide an output voltage of constant magnitude for any selected full scale input deviation.

15. A demodulation system according to claim 13, further including:

tape speed compensation means including;

means for providing a tape reference signal representative of frequency variations of said input signal caused by tape speed variation;

means for delaying said tape reference signal by an amount such to maintain predetermined phase coherence between said tape reference signal and the signal being processed; and

means for adjusting the frequency of the phase lock loop such that frequency error due to tape speed variation is cancelled.

16. An FM demodulation system according to claim 13, further including:

tape speed compensation means including means for providing a tape reference signal representative of frequency variations of said input signal caused by tape flutter;

means for delaying said tape reference signal by an amount such to maintain predetermined phase accuracy between said tape reference signal and the signal being processed; and

means operative in response to said delayed tape reference signal for varying the frequency of said voltage controlled oscillator such to cancel said tape flutter frequency variations.

17. A demodulation system according to claim 7 wherein said reference signal means includes:

means for providing a reference signal of a master frequency, and means for dividing said master frequency to a frequency 1+1/M higher than the center frequency of each stage.

18. An FM demodulation system comprising:

a programmable input low-pass filter having selectable characteristics corresponding to input signal conditions, and adapted to receive an input frequency modulated carrier signal to be processed;

a frequency synthesizer operative to provide a first reference signal of predetermined frequency;

a wide-band mixer adapted to receive a signal from said input low-pass filter and from said frequency synthesizer and to provide in response thereto a signal of a frequency higher than the frequency of said input signal by a predetermined amount;

a plurality of frequency translator stages, each stage having a group of nband-pass filters and a mixer, the center frequency of which is related to the center frequency of the adjacent group by a factor M, the bandwidths of the filters in each group differing by M1/n;

control means coupled to said frequency translator stages for selecting predetermined adjacent ones of said stages and for selecting a predetermined one of said filters in each selected stage, the last selected stage having only a group of band-pass filters associated therewith;

means for applying the signal from said wide-band mixer to the selected filter of the first selected stage;

means operative in reSponse to said first reference signal to provide a reference signal to each mixer of said selected stages of a frequency such that the output signal of each such mixer is the center frequency of the succeeding stage; and

output means operative in response to the signal from said selected filter of said last selected stage to detect the data content of said input modulated carrier signal.

19. An FM demodulation system according to claim 18 wherein M and N each equal 2, and the reference signal applied to each mixer of said selected stages is of a frequency 1 +3/M higher than the center frequency of the respective stages.

20. An FM demodulation system according to claim 18 wherein said reference signal means includes, for each stage, a delay path, whereby the reference signal for each selected stage is generally coherent with said input signal being processed.

21. An FM demodulation system according to claim 18 wherein said reference signal means includes, for each stage, a frequency divider operative to divide said first reference frequency such that the output signal of each mixer of each selected stage is of a frequency equal to the center frequency of the succeeding selected stage.

22. An FM demodulation system according to claim 18 wherein said output means includes an inverter operative in accordance with said control means for selectively inverting the signal from said output means thereby to provide an output signal of uniform polarity irrespective of the number of stages selected.

23. An FM demodulation system according to claim 18 wherein said output means includes:

a limiter coupled to said last selected stage;

a phase-lock loop coupled to the output of said limiter and having a phase demodulator, a programmable loop filter, a voltage controlled oscillator and a programmably frequency divider;

control means for adjusting said frequency divider to provide a loop frequency equal to the center frequency of the last selected stage;

control means for adjusting the characteristics of said loop filter in accordance with input conditions of said modulated input signal;

a programmable output low-pass filter coupled to the output of said phase-lock loop and having selectably characteristics corresponding to input signal conditions;

an inverter coupled to the output of said programmable output low-pass filter and operative to selectively invert the output signal from said output low-pass filter to provide an output signal of uniform polarity irrespective of the number of stages selected; and

a variable gain amplifier coupled to said inverter and operative to provide an output signal of constant magnitude for any selected full scale deviation of said modulated input signal.

24. An FM demodulation system according to claim 23 further including:

means for providing a tape reference signal whose frequency varies correspondingly with frequency variations of said input signal caused by tape speed variation;

means for providing a phase coherent error signal representative of said tape speed variation, said error signal being operative to adjust the frequency of said voltage controlled oscillator such to cancel frequency variations caused by tape speed variation.

25. An FM demodulation system according to claim 23, further including:

tape speed compensation means comprising;

means for providing a tape reference signal representative of frequency variations of said input signal caused by tape speed variation;

means operative in response to said tape reference signal to correspondingly vary the frequency of said first reference signal;

means for delaying said tape reference signal by an amount such to maintain predetermined phase coherence between said tape reference signal and the signal being processed; and

means for adjusting the frequency of the phase-lock loop such that frequency error due to tape speed variation is cancElled.