A device that recovers an original modulated signal from oscillations or waves generated by modulation. Applied disciplines: Communication technology (a subject); communication principles and basic technologies (two subjects). The following figure shows the principle circuit of the demodulator. RL is the load and C is the filter capacitor. Its function is to smooth the output DC voltage. The demodulation switch K and the input AC signal have the same frequency. The following figure shows a half-wave phase-sensitive amplifier circuit, which sets the input signal es to be a sinusoidal voltage and has a phase and frequency with the control voltage Ua. The diode D causes the collector current iC to flow in one direction, and the current is connected in series with negative feedback. When Ua is a positive half wave, both BG and D are in a conducting state, and the collector current iC flows through the load RL, and the output voltage UO is a negative half wave, as indicated by the broken line of the UO waveform diagram, and then smoothed by C. Function, get the DC voltage of the solid line.
It restores the amplified AC voltage to a DC voltage whose magnitude and polarity correspond to the amplitude and phase of the AC voltage. The following figure shows the principle circuit of the demodulator. RL is the load and C is the filter capacitor. Its function is to smooth the output DC voltage. The demodulation switch K and the input AC signal have the same frequency. When Ui is positive, the switch is turned on, and the output is equal to the input voltage UO. After the smoothing of the capacitor C, a smooth DC voltage UO should be obtained. Conversely, if Ui is negative, the switch is turned on, Ui is positive, and the switch is turned off, the output receives a negative pulsating DC voltage UO.
Communication System
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