| 摘要 |
<p>A combined phase-locked loop frequency demodulator and frequency synthesizer for frequency-modulated wave receivers using two phase-locked loops respectively for synthesis and for demodulation. In this device, the frequency-modulated signal is applied to one of the inputs of a first phase comparator whose other input is coupled to the output of a voltage-controlled oscillator, which output is also coupled, through a prescaler and a programmable frequency divider mounted in cascade, to one of the inputs of a second phase and frequency comparator whose other input is coupled to the output of a crystal-controlled reference oscillator. The output of the first comparator is coupled by means of a first low-pass or bandpass filter to a first input of an analog adder whose second input is coupled by means of a second low-pass filter, having a relatively low upper cut-off frequency, to the output of the second comparator. The output of the adder which combines the signals from the two filters is connected to the frequency-control input of the voltage-controlled oscillator. The output of the first filter supplies the demodulated signal and thus constitutes the output of the frequency demodulator, whose phase-locked loop is combined with the phase-locked loop of the frequency synthesizer, which selects the frequency of the modulated carrier wave, by means of the adder and the single voltage-controlled oscillator which are the common elements of both phase-locked loops.</p> |
