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.
Phase-sensitive rectifier demodulator editing 1, half-wave phase-sensitive rectifier The following picture shows a half-wave phase-sensitive rectifier. The reverse-connected (inverted) transistor BG is used as a demodulation switch. The working process is divided into two cases: when Ui and When Ua is in phase, if Ua is left positive and right negative, then BG is saturated (when the transistor is inverted, the PN junction of the C and b poles is added with a forward voltage, which can also reach saturation state), and the output is equal to the positive half wave of the input. Voltage, so the output is positive voltage, but when Ui is inverted with Ua, that is, when Ua is left positive and right negative to make BG saturated, Ui is just positive and negative, so the output is negative DC voltage. . Since the rectified output is related to the phase of Ui, it is called a phase sensitive rectification demodulator. Its output reflects changes in the size and polarity of the input. 2. The full-wave phase-sensitive rectifier demodulator half-wave rectifier can only use the input half-wave voltage, so the demodulation efficiency is low. The following figure shows the full-wave phase-sensitive rectifier circuit. Both BG1 and BG2 adopt ce reverse-connected triodes, which are respectively controlled by two equal-sized, phase-plate inverted voltages Ua1 and Ua2. Let Ui be in phase with Ua. When the positive half wave, Ua1 is left and right negative, so that BG1 is saturated, but Ua2 is left and right negative but BG2 is cut off. At this time, since Ui is also a positive half wave (up and down is negative), Umo is output. It is a positive half wave. Conversely, in the case of a negative half-wave, both Ua1 and Ua2 are left-right and right-right, so that GB1 is cut off and BG2 is smoothed by C, and a smooth and correct output voltage is obtained. Similarly, when Ui is inverted from Ua, a negative output voltage is obtained.
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