US3626311A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Phase lock loop demodulator providing noise suppression
Assignee: Motorola Solutions Inc
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Filing: 1970-07-30
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Granted: 1971-12-07
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Expires: 1990-07-30
Abstract
Abstract A synchronous tone demodulator is comprised of a phase detector, a band-pass filter at the frequency of the desired tone and a low pass filter connected with a voltage-controlled oscillator in a feedback loop from the output of the phase detector to one of two inputs thereof. A carrier wave which is frequency or phase modulated by the tone is applied to the other input of the phase detector. Because the bandwidth of the feedback loop is limited by the filters, noise signals of frequencies outside of the bandpass of the filters are attenuated, thereby allowing the loop to lock even though the signal-to-noise ratio of the modulated wave is low. The desired tone signal derived by the phase detector appears at the output of the band-pass filter.
Inventors
- 👤 Albert V Kraybill
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-22 22:28
CPC Classifications
H; H03; H03D; H03D3/00; H03D3/02; H03D3/24; H03D3/241
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
326 words
A synchronous demodulator for demodulating at least one single frequency tone signal which frequency modulates a carrier wave, the frequency-modulated wave having an average frequency susceptible to drift and being further modulated by noise signals, such demodulator including in combination: phase detector means having first and second input terminals and an output terminal, said first input terminal being connected to receive the frequency-modulated wave; band-pass filter means connected between said output terminal of said phase detector means and a demodulator output terminal and having a first narrow passband which includes the frequency of the tone signal to be demodulated; low pass filter means connected in parallel with said band-pass filter means and having a second narrow passband which includes a frequency equal to the rate of change of the average frequency of the frequency-modulated wave; voltage-controlled oscillator means developing a tracking signal having a center frequency substantially equal to the average frequency of the frequency-modulated wave, and having a tracking frequency control element and an output terminal, said output terminal of said voltage-controlled oscillator means being coupled to said second input terminal of said phase detector means thereby applying said tracking signal thereto; and means coupling the outputs of said band-pass filter means and said low pass filter means to said tracking frequency control element of said voltage-controlled oscillator means for controlling the frequency of the tracking signal; said phase detector means developing a control signal having an amplitude and polarity which varies with the average frequency of the frequency-modulated wave, said low pass filter passing said control signal to said frequency control element so that said tracking signal produced by said voltage-controlled oscillator tracks the average frequency of said frequencymodulated wave, said phase detector means being responsive to said tracking signal and to the frequency-modulated wave to provide the tone and noise signals at the output thereof, said band-pass filter means passing the demodulated tone signal and rejecting the noise signals outside the passband thereof.
Claim 2
Dependent Claim
326 words
A synchronous demodulator for demodulating at least one single frequency tone signal which frequency modulates a carrier wave, the frequency-modulated wave having an average frequency susceptible to drift and being further modulated by noise signals, such demodulator including in combination: phase detector means having first and second input terminals and an output terminal, said first input terminal being connected to receive the frequency-modulated wave; band-pass filter means connected between said output terminal of said phase detector means and a demodulator output terminal and having a first narrow passband which includes the frequency of the tone signal to be demodulated; low pass filter means connected in parallel with said band-pass filter means and having a second narrow passband which includes a frequency equal to the rate of change of the average frequency of the frequency-modulated wave; voltage-controlled oscillator means developing a tracking signal having a center frequency substantially equal to the average frequency of the frequency-modulated wave, and having a tracking frequency control element and an output terminal, said output terminal of said voltage-controlled oscillator means being coupled to said second input terminal of said phase detector means thereby applying said tracking signal thereto; and means coupling the outputs of said band-pass filter means and said low pass filter means to said tracking frequency control element of said voltage-controlled oscillator means for controlling the frequency of the tracking signal; said phase detector means developing a control signal having an amplitude and polarity which varies with the average frequency of the frequency-modulated wave, said low pass filter passing said control signal to said frequency control element so that said tracking signal produced by said voltage-controlled oscillator tracks the average frequency of said frequencymodulated wave, said phase detector means being responsive to said tracking signal and to the frequency-modulated wave to provide the tone and noise signals at the output thereof, said band-pass filter means passing the demodulated tone signal and rejecting the noise signals outside the passband thereof.
Claim 3
Dependent Claim
19 words
The demodulator of claim 1 wherein said tracking frequency control element of said voltage-controlled oscillator means is a varactor.
Claim 4
Dependent Claim
33 words
The demodulator of claim 1 wherein said band-pass filter means includes a mechanically vibratory resonant element which has a mechanical resonant frequency substantially equal to the frequency of the tone to be demodulated.
Claim 5
Dependent Claim
29 words
The demodulator of claim 1 wherein said band-pass filter means includes an active filter means which has a passband that includes the frequency of the tone to be demodulated.
Claim 6
Dependent Claim
16 words
The demodulator of claim 1 wherein said low pass filter means includes an active filter means.
Claim 7
Dependent Claim
45 words
The demodulator of claim 1 for demodulating a plurality of tone signals each having a different predetermined frequency and wherein said band-pass filter means includes a pluraLity of band-pass filters each of which having a narrow passband including one of the tones to be demodulated.
Claim 8
Dependent Claim
18 words
The demodulator of claim 6 wherein all of said band-pass filters are connected in parallel with each other.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1974-12-06 | 1975-06-07 | 1975-12-07 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1978-12-06 | 1979-06-07 | 1979-12-07 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1982-12-06 | 1983-06-07 | 1983-12-07 | $7700.00 | Window Closed / Lapsed |