Hi folks! This week we have introduced the first in a series of analog ICs – the AD633 multiplier IC. 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)

amplitude modulation using AD633

Amplitude Modulation using AD633

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:

amplitude modulation using AD633 output

Amplitude Modulation using AD633 output

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 )

Low Pass filter using AD633

Low Pass filter using AD633

Using the above circuit we get the following output:

Low Pass Filter using AD633 Output

Low Pass Filter using AD633 Output

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:

low pass filter using AD633 output sweep

Low Pass Filter Using AD633 output sweep

So where can we find such a low-pass filter? In some popular electronic music styles, “filter sweeps” have become a common effect. These sweeps are created by varying the cutoff frequency of the VCF (sometimes very slowly) [2]


  1. http://www.analog.com/en/special-linear-functions/analog-multipliersdividers/ad633/products/product.html
  2. http://en.wikipedia.org/wiki/Voltage-controlled_filter