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Principle of Modulator circuits

Published on Dec 20 2010 // Wireless Transmitter Circuits

Principle of Modulator circuits 1

  • Modulators usually have three forms: mechanical modulator (chopper machine), the modulator transistor, FET modulator. Parallel by the circuit can be divided into modulators and series and parallel modulator two, the latter than the former superior performance, but the complex structure.
  • Second, the principle modulator

Principle of Modulator circuits 3  

The figure below shows the schematic modulator, because the switch K load in parallel, it is called parallel controller

Works as follows: If the 0-T / 2 K within the time off, then the A level points achieved UmA; if (T / 2)-T K within the time connected, then A grounding; after the switch with the poor K periodically off action, in A point to get a pulse DC voltage UA (as shown), UA can be divided into DC component and AC component UAO UA-O, after a post blocking capacitor C, UAO landed in the capacitor, while communication sub-UA-up was sent to the load RL, ie UO = UA-O

Third, the parallel modulator1, the transistor modulation controller

Transistor transistor modulator is as switches, the circuit and waveforms shown below, the base of the transistor BG access control voltage Ua (square wave), when a negative half-wave Ua, BG set only, then Ui on C rechargeable battery, charging current is flowing through from top to RL, so the UO is positive; the other hand, when the positive half-wave Ua, BG saturated, then by BG and RL C discharge, the discharge current is too high from the bottom-RL, as it is UO negative. UO alternately with the changes in UO to get the output square wave alternating voltage, its value is proportional to the input voltage, its frequency and Ua the same.

2, FET modulator

Principle of Modulator circuits 2

FET is a FET as a modulator switches, the circuit and waveforms shown below, the figure shows, when the BG of the gate with a negative voltage to the clock Ua, will be able to control the regular opening of FET and the pinch-off, thus the input DC voltage into AC output voltage Ui UO, work process and the same transistor modulator.

Four, series-parallel modulator

The following figure (a) for the series-parallel modulator and its waveform. In series with the load RL BG1, BG2 and RL parallel, the two FET BG1, BG2, respectively controlled by the voltage Ua1 and Ua2; and Ua1 and Ua2 on location, the phase contrast, if 0 – (T / 2) time the Ua1 is positive, the Ua2 is negative, so that BG1 and BG2 turn off, if this time Uw = Ui (T / 2) / T time Ua1 is negative, the Ua2 is positive, so that BG1 and BG2 conduction cut-off at this time, UW = 0. Through the coupling capacitor C2, the filter DC component in the UW, in the negative has been cut at both ends of the exchange of RL square wave modulation,

The following figure (b), is a two DC input signals (Ui and Uf) of the series and parallel modulator and its waveform, which can simultaneously prepared and compared two tasks, the output voltage UO is proportional to the magnitude of the two input signal Diao poor, working principle and the same