AD633 Analog multiplier

The AD633 is an IC that can do analog calculations, like multiplication, division, exponentiation and also square rooting, which we need for our octave divider.

The circuit below (taken from the datasheet, figure 15) represents the square root operation for a sine wave. Note that the sine wave should not cross the zero volt line! For the most “perfect” operation, the sine wave should actually touch the zero volt line. The diode will prevent any reverse voltage.

According to the datasheet, the AD633 needs at least a dual power ±8V supply, so if we want to use a regular 9V single power source as is custom in a stompbox, some extra components are needed in the power section (see the mu-tron section). The resulting waveform is presented below. The red signal is the original input signal (always below zero), the green signal is the square root output.