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In school I have learned in both systems and communication about multiplication blocks. I have been taught that these blocks create a sum and difference frequency and can be filtered to get just the sum or the difference.

What I am wondering is how to actually implement a block like this in hardware. I first thought about an OPAMP multiplier setup, but I didn't think something like this worked well for high frequencies like 900MHz or 2.4GHz. How do I go about finding a device that will do this block for me?

  • Take a look at the fundamentals video about the Gilber cell. The only prerequisite is that you understand long tailed pairs of differential amplifiers. https://www.youtube.com/watch?v=7nmmb0pqTU0 – jippie Dec 22 '15 at 20:10

2 Answers2

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Lookup "Gilbert Cell" and "Four quadrant multiplier".

More generally, look into "translinear circuits" which are more general, the multiplier being a special case. The key idea is the logarithmic relation between the base-emitter voltage and emitter current. Some number of transistors are connected with their base-emitter junctions in a loop. By Kirchoff's voltage law, the sums of voltages around this loop is zero, and by the logarithmic relation, you can say something useful about the product of emitter currents. With cleverness in making use of that fact, you can design a multiplier. Differential amplifiers are a relevant idea, just not the key idea.

Some articles:
http://www.analog.com/library/analogdialogue/archives/42-11/multipliers.html
http://en.wikipedia.org/wiki/Translinear_circuit

and find the paper "Translinear Circuits" by Barrie Gilbert

and for a good read that covers much more but includes a nice little explanation of translinear circuits, look for the article "The Gears of Genius" in IEEE SOLID-STATE CIRCUITS SOCIETY NEWS, Fall 2007 issue. This article is followed by one describing a very fast multiplier circuit.

Connor Wolf
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DarenW
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The SA612 is a popular device using a Gilbert cell multiplier; it's often used by radio amateurs for simple superhet and direct-conversion radio receivers. It won't go up to 900 MHz or 2.4 GHz, but is suitable for experimentation at HF and VHF.

Leon Heller
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