# RF Mixers

Discussion in 'Electronic Basics' started by Don, Jul 22, 2003.

1. ### DonGuest

Does anyone know of a web page that describes the purpose and
operation of RF mixers? Best I have been able to tell that given two
frequencies, a mixer generates the sum and difference.

Thanks!

Don

2. ### A EGuest

Yes, that's right. Check here for some more fun:
http://www.minicircuits.com/application.html
and scroll down some.

5. ### Robert LacosteGuest

There was an article in Circuit Cellar 2-3 months ago...
You can also find a good application note on www.minicircuits.com
(describing more the parameters of mixers)

Cheers,

Robert Lacoste - ALCIOM : The mixed signals experts
http://www.alciom.com

6. ### Precious PupGuest

Others have some pointers. Try Synergy Microwave too. They have some app notes.

Mixers, RF or otherwise, are schematically represented by an X. *The X literally means multiplication*. That
is, multiplication in the time domain (or convolution in the frequency domain).

For example, you have 2 sinusoids applied to the two "input" ports of a mixer (for some passive mixers I's and
O's are interchangable).

x1(t) = cos(w1·t)
x2(t) = cos(w2·t)

So the mixer literally does:

mixer_out = x1(t)·x2(t) = cos(w1·t)·cos(w2·t)

and by trig identity, we then have

x1(t)·x2(t) = 0.5·cos([w1-w2]·t) + 0.5·cos([w1+w2]·t)

So there you see the mathematical result explaining "sum and difference" frequencies. There is usually a
little more to it on account of the fact that RF mixers often have one of the ports "overdriven" or run in the
"switch mode" (the "LO" port). See the links.