Amplitude Modulation

Posted on Feb 5, 2014

This is a functionally complete, four-quadrant, analog multiplier. Four quadrant means that both operands that are multiplied can take any polarity i. e. +/- and hence multiplication can happen across 4 quadrants. It includes high impedance, differential X and Y inputs, and a high impedance summing input (Z). Thus this multiplier basically does a MAC operation

(Multiply and Accumulate). The AD633 is well suited for such applications as modulation and demodulation, automatic gain control, power measurement, voltage-controlled amplifiers, and frequency doublers. The input range of operating voltages for this IC is from +15 V to -15 V. So while designing circuits with AD633 keep in mind that the inputs do not exceed this limit. Typically this IC provides a bandwidth of 1 MHz. [1] Let`s check out a few applications using AD633 on DoCircuits. First up, given below is an amplitude modulator circuit. ( Click on the circuit to load it on DoCircuits) The carrier and modulation inputs to the AD633 are multiplied to produce a double sideband signal. The carrier signal is fed forward to the Z input of the AD633 where it is summed with the double sideband signal to produce a double sideband with the carrier output. Here is how the AM signal generated looks like: Another very simple application using the AD633 is the voltage controlled low pass filter. The cutoff frequency is modulated by EC, the control input. ( Click on the circuit to load it on DoCircuits ) Now to show how you can control this low-pass filter we can sweep the control voltage (Vdc) from 0. 01 V to 0. 02 V (this is done by selecting Frequency Domain Analysis and enabling the sweep settings. Then vary the Vdc values as given) and plot the frequency response as shown: So where can we find such a low-pass filter In some popular...

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