| 摘要 |
In two circuit arrangements for demodulating RF signals which are supplied to one input of a mixer M, the output of the mixer M is connected to the input of a narrow-band band-pass filter B. In one circuit arrangement, the output of the band-pass filter B is connected to the phase detector PD of a PLL circuit, the voltage-controlled oscillator VCO of which is connected to the other input of the mixer M. The demodulated output signal can be picked up at the output of the low-pass filter TP of the PLL circuit. In the other circuit arrangement, the output of the band-pass filter B is connected to the input of a demodulator D, the output of which is connected to the input of a voltage-controlled oscillator VCO. The output of the voltage-controlled oscillator VCO is connected to the other input of the mixer M. Because the frequency f2 at the output of the mixer M is controlled to a constant value by the voltage-controlled oscillator VCO in both circuits, a band-pass filter with a very narrow bandwidth can be used. The narrower the bandwidth of the band-pass filter, the better will be the signal/noise ratio. <IMAGE>
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