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Demodulator circuit

Published on Dec 20 2010 // Wireless Transmitter Circuits

Demodulator Circuit 1

st, the working principle of the demodulatordemodulator is modulated dc amplifier circuit is an important component. It has enlarged the reduction of AC voltage to DC voltage, the size and polarity and AC voltage to the corresponding amplitude and phase.

Below is the principle of the demodulator circuit, RL is the load, C the filter capacitor, its role is to smooth the output DC voltage, demodulator switch K and the input AC signal, Ui has the same frequency. When Ui is positive, the switch is turned on, the output is equal to the input voltage UO, through the smoothing capacitor C, should obtain a smooth DC voltage UO. Conversely, if Ui is negative, the switch is turned on, Ui is positive, switch off, then get a negative pulse output DC voltage UO.

Second, the phase sensitive rectifier demodulator1, the phase-sensitive half-wave rectifier Half-wave phase-sensitive below shows rectifier to Ce reverse (inverted) and BG for demodulator transistor switches, the working process in two ways: when Ui and Ua is the same phase, if the left is the right Ua negative, then the BG Saturation (inverted transistors work, C pole and b pole PN junction forward voltage increases, the same can reach saturation), the output is equal to the input of the positive half wave voltage, so the output voltage polarity is positive, but RP when Ui and Ua, that is, when is the right Ua negative to the left BG saturated, Ui exactly is under the negative, so the DC output is negative voltage. Since the phase rectifier output and Ui is related to so called phase sensitive rectifier demodulator. Its output can reflect the size and polarity of the input changes.

Demodulator Circuit 2

2, full-wave rectifier phase sensitive demodulator

Half-wave rectifier can only use half-wave voltage input, low efficiency and therefore demodulation, the next picture shows the full wave phase sensitive rectifier. BG1, BG2 ce reverse transistors are used, respectively, by two equal and opposite voltage Ua1 phase plates and Ua2 control. Let Ui and Ua-phase, half wave Ua1 left is the right negative, the saturation BG1 connected, but the negative is BG2 Ua2 closing left and right, this time, as also for the positive half-wave Ui (up and down is negative), so the output Umo positive half-wave. Conversely, the negative half-wave,, Ua1 and Ua2 are negative the right is left, so close and BG2 GB1 smoothed by C, can be a smooth proper output voltage. Similarly, when Ui and Ua RP, then get a negative output voltage.

Demodulator Circuit 3

Third, the phase sensitive demodulator amplification1, half-wave phase-sensitive amplifier

Demodulator Circuit 4

Above the phase-sensitive rectifier demodulator, only the role of the input signal from the modem, no amplification of resistance, the next picture shows the half-wave phase-sensitive amplifier, set the input signal is sinusoidal voltage es and a phase and control phase voltage Ua and frequency, diode D so that the collector current iC-way flow of Re from the current series of negative feedback

When es and Ua are positive half-wave, the BG and D are in a conduction state, the collector current iC flows through the load RL, the output voltage UO is negative half-wave, such as the dotted line waveform shown in UO, and then by C of the smoothing effect of the DC voltage by the solid line. Amplification of the BG, so the power supply load RL input power base rather than by the demodulated voltage Ua for energy by the load. In the figure above that if the input es es and Ua is the next on the negative, and Ua is negative for the next on the positive, although D still positive bias, but the BG end, it ic is zero, the output is also zero. Therefore, the output signal of the input signal and the phase-sensitive amplification, it is called phase-sensitive amplifier.

The figure is DDZ-11 type instruments in the practical phase-sensitive amplifiers, the following diagram A, the input AC signal is Ui, the feedback signal output AC transformer B3, B2 demodulation input voltage Ua by the transformer and by the regulator DW1, DW2 limit amplitude, so that A, B side peaks between two points – set at 18 volts peak, R2 is a regulator of the current limiting resistor. When Ua, Ui for the anti-bias, ib and ic are zero. With Ui, Ua cycle changing. iC is a pulsating DC, can be decomposed into a constant DC IC and AC iC-, which flows through the RL into a demodulator IC DC voltage and AC component iC-B3 was obtained by the feedback voltage transformer] UF.

When Ui, Ua into reverse, io and ic is equal to zero, indicating that the phase-sensitive amplifier role

Demodulator Circuit 5

The figure is DDZ-11 type instruments in the practical phase-sensitive amplifiers, the following diagram A, the input AC signal is Ui, the feedback signal output AC transformer B3, B2 demodulation input voltage Ua by the transformer and by the regulator DW1, DW2 limit amplitude, so that A, B side peaks between two points – set at 18 volts peak, R2 is a regulator of the current limiting resistor. When Ua, Ui for the anti-bias, ib and ic are zero. With Ui, Ua cycle changing. iC is a pulsating DC, can be decomposed into a constant DC IC and AC iC-, which flows through the RL into a demodulator IC DC voltage and AC component iC-B3 was obtained by the feedback voltage transformer] UF.

When Ui, Ua into reverse, io and ic is equal to zero, indicating that the phase-sensitive amplifier role

Demodulator Circuit 6

2, full-wave phase-sensitive amplifier

The following picture shows the full-wave phase-sensitive amplification power, the figure for the DC motor M of the stator windings, obtained by the demodulation signal is driven by DC motor rotation to perform the terminal display tasks. Works follows: if Ui and Ua-phase, when Ui and Ua is a positive half-wave, BG conduction current iL from the A D1 BG  Re D3 M  B by, iL positive half-wave, located motor M is transferred; the contrary, when Ui and Ua negative half-wave, BG anti-bias cut-off, so iL zero (see Figure b)