Single transistor mixer

ChesterW · 2016-02-21T22:22:20+00:00

I need to make a mixer (a multiplier, not an adder) for sinusoid signals somewhere between about 10 kHz and 1 Mhz. This is for a lock-in-amp. My main constraint is low cost. I'd use a microcontroller with an A to D and a hardware multiplier, but I'd like to keep the cost down by using a cheaper micro. I could use a simple power-of-2 window in the micro and then only need additions to demod, but that would give me a wider bandwidth for noise to get in. I though a single transistor mixer design might give better results. Anyone know of a good reference? ChesterW +++ Dr Chester Wildey Founder MRRA Inc. Electronic and Optoelectronic Instruments MRI Motion, fNIRS Brain Scanners, Counterfeit and Covert Marker Detection Fort Worth, Texas, USA wildey at mrrainc dot com

Feb 21, 2016 61 Replies

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bill.sloman 10 years ago

something that is sold as

It's a marketing distinction, not a technological distinction. Every four quadrant multiplier is a potential mixer, but they tend not to be sold as such.

Bill Sloman, Sydney

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ChesterW 10 years ago

I estimate using a sine for demod would give only about 1 dB improvement over square wave demod for uncorrelated noise. For correlated noise it should be in the neighborhood of 7 dB. I think you're right that the lions share of the improvement is getting out of the baseband.

My newsreader seems to have lost some of my replies to everyone. Anyway, thanks for the help.

ChesterW

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