I need to get information about multiplier circuits.
What sort of multipliers?
There are voltage multipliers, frequency multipliers, photo multipliers, digital multipliers.
Wikipedia lists a lot more.
I was suppose to say Analog multipliers.
What do you find when you use Google or wikipedia.org? We would prefer that you ask an informed question here, rather than an open-ended question with many long answers possible. Especially if it is for schoolwork.
Look at the Analog Devices 250 MHz, 4 quadrant AD835 analog multiplier.
You might try researching under Gilbert cell. Barrie Gilbert is the inventor of the multiplier. He came up with it as variable gain control for use in Tek scopes.
There are two incarnations out there. One is a six transistor design that is used for RF mixing (reference SA612). These are not suited to analytic functions because they lack the distortion reduction circuitry found in Gilbert's original design.
The following site has the internal schematic for Gilbert's original multiplier:
The circuit is on page 5 and the critical elements are the two transistors in the upper left corner. They pre-distort the voltage to the multiplier cell, thus linearizing it.
In addition to this circuit, there is the one quadrant multiplier, which is based on log and antilog amps. National has a good treatment on this:
There are other techniques as well, such as converting value x into a PWM and using it to actuate an analog switch to chop between value y and 0 volts. The output is then filtered to remove the high frequency noise from the PWM carrier.
In all these techniques, though, none is as cost effective and stable as pulling you signal into the digital domain. I've repeatedly started to use an analog method, and I keep going back to digital.
Here is the patent from 1962 describing the first analog multiplier:
Here is a multiplier (mixer) using four diodes. I show it multiplying 550 kHz and 5.5 MHz.
There were earlier multipliers that used potentiometers tied to servo motors (god help it if a piece of dirt got in the servo pot!)
There was also the parabolic multiplier, which used long strings of resistors and diodes to approximate x^2.
ab = [ (a+b)^2 - (a-b)^4 ] / 4
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