US3584154A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Stereo multiplex decoding system with a phase locked loop switching signal control
Assignee: Individual
•
Filing: 1968-06-17
•
Granted: 1971-06-08
•
Expires: 1988-06-17
Abstract
Abstract A stereo decoding system for FM receivers that is compatible with integrated circuit techniques and contains a phase locked loop to provide stability for the demodulator switching signal. Carrier noise is maintained at a minimum by a narrow equivalent band pass filter and in particular embodiments no inductors are required.
Inventors
- 👤 Clarence Hunter Mcshan
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-25 23:41
CPC Classifications
H; H03; H03D; H03D1/00; H03D1/22; H03D1/2209; H03D1/2236
Claims Analysis
Total Claims: 21
Claim 1
Independent Claim
260 words
In a system for decoding a composite stereophonic signal having signal components in a band of lower frequencies, signal components in a separate band of higher frequencies and a pilot subcarrier signal at a frequency intermediate said bands, the combination of first filter means effective to pass said pilot subcarrier signal and at least attenuate frequencies below said pilot subcarrier signal, control signal responsive means for generating a first local signal with a frequency that is a multiple of the frequency of said pilot subcarrier signal, frequency divider means responsive to said local signal generating means for generating at least one other local signal in phase locked relation to said first local signal and of the same frequency as said pilot subcarrier signal, signal sampling means connected to receive said pilot subcarrier signal from said filter means and rendered operative periodically by said other local signal for supplying to said first local signal generating means a control signal representative of periodically selected samples of said pilot subcarrier signal so as to maintain said first and other signals in phase locked relation to said pilot subcarrier signal, second filter means interposed between said sampling means and said control signal responsive generating means for passing to the latter onLy signals of frequency less than or equal to the difference between the frequency of said pilot subcarrier signal and the frequency of said other local signal, and means jointly responsive to said composite signal and to a multiple of said other local signal for separating said composite signal into different information containing components.
Claim 2
Dependent Claim
260 words
In a system for decoding a composite stereophonic signal having signal components in a band of lower frequencies, signal components in a separate band of higher frequencies and a pilot subcarrier signal at a frequency intermediate said bands, the combination of first filter means effective to pass said pilot subcarrier signal and at least attenuate frequencies below said pilot subcarrier signal, control signal responsive means for generating a first local signal with a frequency that is a multiple of the frequency of said pilot subcarrier signal, frequency divider means responsive to said local signal generating means for generating at least one other local signal in phase locked relation to said first local signal and of the same frequency as said pilot subcarrier signal, signal sampling means connected to receive said pilot subcarrier signal from said filter means and rendered operative periodically by said other local signal for supplying to said first local signal generating means a control signal representative of periodically selected samples of said pilot subcarrier signal so as to maintain said first and other signals in phase locked relation to said pilot subcarrier signal, second filter means interposed between said sampling means and said control signal responsive generating means for passing to the latter onLy signals of frequency less than or equal to the difference between the frequency of said pilot subcarrier signal and the frequency of said other local signal, and means jointly responsive to said composite signal and to a multiple of said other local signal for separating said composite signal into different information containing components.
Claim 3
Dependent Claim
36 words
A stereophonic decoding system according to claim 1, wherein said first local signal generating means comprises an oscillator and the frequency divider means is synchronized and in phase locked relation with the output of said oscillator.
Claim 4
Dependent Claim
83 words
A stereophonic signal decoding system as in claim 2, in which said signal sampling means functions as a switch with equal ON and OFF periods in response to the output of said divider means at a 19 kilohertz switching rate and in 90* out-of-phase relation to said pilot subcarrier, and with said signal sampling means being coupled by a constant driving impedance means to said second filter means, all to reject effectively undesired intermodulation products in the output of said second filter means.
Claim 5
Dependent Claim
42 words
A stereophonic signal decoding system as in claim 3, in which said signal sampling means comprises bidirectional solid state switching means in which the output of said divider means is substantially isolated from the input and output of said signal sampling means.
Claim 6
Dependent Claim
49 words
A stereophonic signal decoding system according to claim 4, wherein said frequency divider means is bistable circuit means that changes state responsive to the output of said oscillator, whereby said signal sampling means is effective to extract samples of said pilot subcarrier signal passing through said first filter means.
Claim 7
Dependent Claim
18 words
A stereophonic signal decoding system according to claim 5, including limiting means at the output of said oscillator.
Claim 8
Dependent Claim
65 words
A stereophonic signal decoding system according to claim 1, wherein said first local signal generating means comprises an oscillator providing an output signal having a nominal frequency that is an integral multiple of the frequency of said pilot subcarrier, and a plurality of frequency divider means responsive to the output of said oscillator are provided for reducing said nominal frequency to said pilot subcarrier frequency.
Claim 9
Dependent Claim
46 words
A stereophonic signal decoding system according to claim 7, including control means responsive to the outputs of said frequency divider means to selectively modify the cutoff frequency of said second filter means when the output of said divider means is synchronized with said pilot subcarrier signal.
Claim 10
Dependent Claim
81 words
A stereophonic signal decoding system according to claim 8, wherein said control means includes means for adding the outputs of said frequency divider means, unidirectionally conductive means supplied by the output of said first filter means and controlled by the output of said adding means to selectively pass the output of said first filter means, and third low pass frequency filtering means responsive to the output of said unidirectionally conductive means to provide the control signal for modifying said cutoff frequency.
Claim 11
Dependent Claim
60 words
A stereophonic signal decoding system according to claim 9, wherein the output of one of said frequency divider means and said composite stereophonic signal is supplied to said composite signal separating means, and wherein said stereo separating means includes means controlled by said control means to separate the components of said composite signal only when said pilot subcarrier is present.
Claim 12
Dependent Claim
86 words
A stereophonic signal decoding system according to claim 10, wherein said composite signal separating means comprises a plurality of bidirectional solid state switching means connected to receive said composite signal, said switching means including means substantially isolating said second control signal from the input and output of said switching means, and said switching means being rendered successively conductive and nonconductive for equal time periods under control of one of said frEquency dividing means to pass samples of said composite signal alternately to separate signal component channels.
Claim 13
Dependent Claim
23 words
A stereophonic signal decoding system according to claim 11, wherein each of said bidirectional switching means has buffer means at the output thereof.
Claim 14
Dependent Claim
23 words
A stereophonic signal decoding system according to claim 12, wherein the outputs of said buffer means are cross-coupled to cancel unwanted signal components.
Claim 15
Dependent Claim
45 words
A stereophonic signal decoding system according to claim 13, wherein the output of each filter means includes deemphasis filter means to remove switching ripple introduced by the operation of said bidirectional switching means, said buffer means presenting constant driving impedance to said deemphasis filter means.
Claim 16
Dependent Claim
70 words
A stereophonic signal decoding system according to claim 14, in which each buffer means comprises transistor amplifier means coupled to each output of said switching means and having collector and emitter outputs 180* phase related, deemphasis low pass filter means is coupled to each collector, and a portion of the emitter output of each amplifier means is to the collector of the other amplifier means to secure maximum signal separation.
Claim 17
Dependent Claim
94 words
A stereophonic signal decoding system according to claim 15, in which the means for automatically reducing the cutoff frequency of said second filter means when synchronization occurs comprises controllable rectifier means coupled to the output of said first filter means, said rectifier means being controlled by a 19 kilohertz signal derived from said divider means whereby said rectifier means produces a DC signal output when said pilot subcarrier signal is present and when synchronization occurs, and means responsive only to said DC signal output for reducing the cutoff frequency of said second filter means.
Claim 18
Dependent Claim
28 words
A stereophonic signal decoding system as in claim 16, together with means for rendering said switching means conductive when said first filter means receives a monaural signal input.
Claim 19
Dependent Claim
22 words
A stereophonic decoding apparatus according to claim 16, wherein said DC signal transfers the separation means from monaural operation to stereo operation.
Claim 20
Dependent Claim
20 words
A stereophonic decoding system according to claim 16, wherein said DC signal is also used to actuate stereophonic indicator means.
Claim 21
Dependent Claim
35 words
A stereophonic decoding apparatus according to claim 16, wherein the cutoff frequency of said second filter means is altered by altering an electrical component in said second filter means in response to said control signal.
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) | 1974-06-07 | 1974-12-07 | 1975-06-08 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1978-06-07 | 1978-12-07 | 1979-06-08 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1982-06-07 | 1982-12-07 | 1983-06-08 | $7700.00 | Window Closed / Lapsed |