FM demodulation and frequency tuning for a phase-locked loop
AssigneeSGS-Thomson Microelectronics S.A.
InventorPascal Mellot
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Abstract
The invention provides a demodulation PLL wherein: the first position of a switch, which is controlled by a control circuit, respectively connects the outputs of a mixer and a LP filter to high gain and low gain inputs of an oscillator when frequency signals at the inputs of the mixer have not converged sufficiently, i.e. during the PLLs tuning mode; the second position of the switch respectively connects the outputs of the mixer and the LP filter to the low gain and high gain inputs of the oscillator when the frequency signals at the inputs of the mixer and the signal levels on the input and output of the filter have converged sufficiently, i.e. during the PLLs demodulation mode.
Claims34
A controlled oscillator for providing an output signal, comprising:
- a current controlled oscillator;
- a first input, for receiving a high gain control signal;
- a second input, for receiving a low gain control signal;
- and
- first and second voltage controlled current sources, coupled to said current controlled oscillator, each having a control input, with the control input of said first voltage controlled current source being coupled to said high gain control input and the control input of said second voltage controlled current source being coupled to said low gain control input.
A demodulation phase-locked loop, comprising:
- a mixer having a first input for receiving an input signal;
- a controlled oscillator connected to the mixer, said controlled oscillator having a low gain control input, a high gain control input and an output connected to a second input of said mixer;
- a controlled switch, having a first position for coupling said low gain control input of said controlled oscillator to a first signal line, and for coupling said high gain control input of said controlled oscillator to a second signal line, and having a second position for coupling said high gain control input to said first signal line, and said low gain control input to said second line, wherein said position of said switch is selected according to an operating mode of said phase-locked loop.
A demodulation phase-locked loop, comprising:
- a mixer having a first input for receiving an input signal;
- a controlled oscillator connected to the mixer, said controlled oscillator having a low gain control input, a high gain control input and an output connected to a second input of said mixer;
- a controlled switch, having a first position for coupling said low gain control input of said controlled oscillator to a first signal line, and for coupling said high gain control input of said controlled oscillator to a second signal line, and having a second position for coupling said high gain control input to said first signal line, and said low gain control input to said second line, wherein said position of said switch is selected according to an operating mode of said phase-locked loop;
- and
- a control unit, coupled to said controlled switch, to select said position of said controlled switch such that said controlled oscillator provides a high gain output when said switch is in said first position, and said controlled oscillator provides a low gain output when said switch is in said second position.
A method for tuning a demodulating phase locked loop, said demodulating phase locked loop coupled to receive a carrier signal including an input signal and provide an output signal, the method comprising the steps of:
- mixing a voltage controlled signal with the input signal to provide the output signal, wherein the voltage controlled signal is provided by a voltage controlled oscillator having a high gain input and a low gain input;
- operating said phase locked loop in a tuning mode of operation during which said phase locked loop is tuned to a first frequency of said carrier signal by coupling said high gain input to a first signal line and said low gain input to a second signal line;
- and
- switching said phase locked loop to operate in a demodulation mode of operation by coupling said high gain input to said second signal line and said low gain input to said first signal line, including the step of demodulating said input signal from said carrier signal to provide said output signal responsive to said phase locked loop being tuned to said first frequency of said carrier signal.
Dependencies are inferred from the claim text.