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US 5,631,601 AGranted
FM demodulation with a variable gain phase locked loop
AssigneeSGS-Thomson Microelectronics S.A.
InventorsWayne L. Horsfall, Gary Shipton
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AssigneeSGS-Thomson Microelectronics S.A.
InventorsWayne L. Horsfall, Gary Shipton
Estimating the term…
A method of demodulating an FM carrier wave and an FM demodulation circuit are described which use a phase locked loop. An FM input signal including the carrier wave is supplied to a phase detector in the phase locked loop. The output of the phase detector is filtered and used to generate a signal for use in controlling a voltage controlled oscillator having an output also connected to the phase detector. The phase locked loop is tuned to a selected carrier wave frequency and a variable gain setting of a variable gain circuit in the phase locked loop is selected to select a desired loop gain. The signal for use in controlling the voltage controlled oscillator is varied by the variable gain circuit to alter the amount by which the frequency of the output of the voltage controlled oscillator changes in relation to a given output of the phase detector. The variable gain setting is selected to select a required bandwidth for demodulation.
A method of demodulating an FM carrier wave to generate a demodulated audio signal by use of a phase locked loop circuit in which an FM input signal including said carrier wave is supplied to a first input of a phase detector, the output of the phase detector being filtered by a loop filter and used to generate a signal for use in controlling a voltage controlled oscillator having an output connected to a second input of said phase detector, which method comprises tuning the phase locked loop circuit to a selected carrier wave frequency, said tuning including selecting a variable gain setting of a variable gain circuit in the phase locked loop to select a desired loop gain, wherein said signal for use in controlling the voltage controlled oscillator is varied by said variable gain circuit to alter the amount by which the frequency of the output of the voltage controlled oscillator changes in relation to a given output of the phase detector, the variable gain setting being selected to select a required bandwidth for demodulation, and wherein the filtered output of the phase detector represents said demodulated audio signal.
A phase locked loop circuit for demodulating an FM carrier wave to generate a demodulated audio signal which circuit comprises a phase detector having a first input for receiving said FM carrier wave, a filter for filtering an output of the phase detector and a voltage controlled oscillator responsive to the filtered output of the phase detector and arranged to provide a second input to the phase detector for comparison with said FM carrier wave, said circuit including a variable gain circuit operable to select a desired gain for the phase locked loop, wherein said filtered output of the phase detector is varied by said variable gain circuit to alter the amount by which the frequency of the output of the voltage controlled oscillator changes in relation to a given filtered output of the phase detector thereby selecting a bandwidth for demodulation by the circuit, and wherein the filtered output of the phase detector represents said demodulated audio signal.
An FM demodulator for audio signals, which demodulator includes a phase locked loop circuit comprising a phase detector having a first input for receiving an FM carrier wave, a filter for filtering an output of the phase detector and a voltage controlled oscillator responsive to the filtered output of the phase detector and arranged to provide a second input to the phase detector for comparison with said FM carrier wave, said circuit including a variable gain circuit operable to select a desired gain for the phase locked loop, wherein said filtered output of the phase detector is varied by said variable gain circuit to alter the amount by which the frequency of the output of the voltage controlled oscillator changes in relation to a given filtered output of the phase detector thereby selecting a bandwidth for demodulation by the circuit, and wherein the filtered output of the phase detector represents a demodulated audio signal.
A demodulating circuit for generating an audio signal from an FM carrier wave, which circuit comprises a gain control circuit for receiving an FM signal, a phase locked loop circuit coupled to the gain control circuit for locking onto a selected carrier wave frequency, said phase locked loop comprising a phase detector having a first input for receiving said FM carrier wave, a filter for filtering an output of the phase detector and a voltage controlled oscillator responsive to the filtered output of the phase detector and arranged to provide a second input to the phase detector for comparison with said FM carrier wave, said circuit including a variable gain circuit operable to select a desired gain for the phase locked loop, wherein said filtered output of the phase detector is varied by said variable gain circuit to alter the amount by which the frequency of the output of the voltage controlled oscillator changes in relation to a given filtered output of the phase detector thereby selecting a bandwidth for demodulation by the circuit, the filtered output of the phase detector representing said audio signal and including an amplitude detector for detecting amplitude variation in said selected carrier wave and providing a tuned gain control signal, said amplitude detector being coupled to said gain control circuitry to control the gain of said gain control circuit when the phase locked loop is locked onto the selected carrier wave.
Dependencies are inferred from the claim text.