Patent US3774469A successfully refreshed from Google Patents.
Patent US4605904A successfully refreshed from Google Patents.
US4605904A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Phase locked loop frequency demodulator having an adjustable bandwidth
Assignee: US Philips Corp
•
Filing: 1985-05-08
•
Granted: 1986-08-12
•
Expires: 2005-05-08
Abstract
Abstract Video frequency demodulator having a phase-locked loop (P.L.L.) intended more specifically for receiving signals transmitted via satellites, in which the bandwidth of the loop is adjusted as a function of the signal/noise ratio for adapting the demodulation threshold. Measuring the signal/noise ratio is realized by sampling (10, 12, 25) briefly the demodulated output signal (13) at the beginning of a picture field scan, rectifying this signal (10) and comparing (7) the stored rectified signal (14) to a predetermined voltage value (21). The signal coming from the comparator (16) is applied to the gain-control input of a variable-gain amplifier (6) incorporated in the control loop.
Inventors
- 👤 Mohammed Hajj-Chehade
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 09:45
CPC Classifications
H; H04; H04N; H04N7/00; H04N7/04; H04N7/045; H03; H03D; H03D3/00; H03D3/02; H03D3/24; H03D3/241; H03D2200/00; H03D2200/0001; H03D2200/0025
Claims Analysis
Total Claims: 7
Claim 1
Independent Claim
125 words
A frequency demodulator whose bandwidth can be adjusted during operation, used in a TV picture receiver receiving inter alia synchronizing signals, this demodulator being of the phase control loop type formed in essence by a phase comparator, a filter and a voltage-controlled oscillator, characterized in that it comprises a sampling circuit for taking a sample of the demodulated signal from the output of the demodulator at the start of a synchronizing signal, the sampling circuit comprising a rectifier for rectifying said sample signal, a comparator for comparing the rectified sample signal with a predetermined d.c. voltage, and in that the output of this comparator which produces a correction signal is coupled to a variable gain input of a variable-gain amplifier included in the control loop.
Claim 2
Dependent Claim
125 words
A frequency demodulator whose bandwidth can be adjusted during operation, used in a TV picture receiver receiving inter alia synchronizing signals, this demodulator being of the phase control loop type formed in essence by a phase comparator, a filter and a voltage-controlled oscillator, characterized in that it comprises a sampling circuit for taking a sample of the demodulated signal from the output of the demodulator at the start of a synchronizing signal, the sampling circuit comprising a rectifier for rectifying said sample signal, a comparator for comparing the rectified sample signal with a predetermined d.c. voltage, and in that the output of this comparator which produces a correction signal is coupled to a variable gain input of a variable-gain amplifier included in the control loop.
Claim 3
Dependent Claim
35 words
A demodulator as claimed in claim 1, characterized in that it comprises a field frequency divider, so as to take a sample during one single field synchronizing signal out of a plurality of such signals.
Claim 4
Dependent Claim
29 words
A demodulator as claimed in claim 1, characterized in that it comprises a memory for storing the value of one of the rectified sampling signal and the correction signal.
Claim 5
Dependent Claim
54 words
A demodulator as claimed in claim 1, characterized in that said variable-gain amplifier is formed by two parallel paths, one for the lower frequencies and the other for the higher frequencies, the path intended for the higher frequencies has a variable gain, while the path intended for the lower frequencies has a fixed gain.
Claim 6
Dependent Claim
51 words
A demodulator as claimed in claim 1, comprising inter alia, upstream of the phase comparator in the path through which the signal to be demodulated flows, a variable-gain intermediate-frequency amplifier, characterized in that the correction signal originating from the comparator is also conveyed to said intermediate-frequency amplifier for controlling its gain.
Claim 7
Dependent Claim
52 words
A demodulator as claimed in claim 1, characterized in that said predetermined d.c. voltage used in the comparator is obtained in a measuring circuit (24) by adding together a d.c. voltage which is proportional to the amplitude of the useful video signal and a constant d.c. voltage of a predetermined fixed value.
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) | 1989-08-11 | 1990-02-10 | 1990-08-12 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1993-08-11 | 1994-02-10 | 1994-08-12 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1997-08-11 | 1998-02-10 | 1998-08-12 | $7700.00 | Window Closed / Lapsed |