1. Home
  2. Electronics Design
  3. Multiplier VS. mixer
  4. Page 2

Multiplier VS. mixer

You're describing an open circuit.

A double-balanced mixer, when it's terminated to be a unidirectional device and driven nice and hard, should produce something like

y_IF(t) = x_RF(t) * signum(sin(w_LO * t)),

where signum(x) = -1 for x < 0, signum(x) = 1 for x > 0 and don't ask me about x = 0. So there is most definitely a signal coming out of y_IF for any signal x_RF going in.

You probably mean there isn't a _component_ of y_IF at the _frequency_ of x_RF without a peculiar combination of RF and local oscillator frequency. That is the case but that's not what the definition speaks to.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Reply to
Tim Wescott
Loading thread data ...

Look at the original posting. The man is talking about frequency. Yes, I have used 1496s since the day thay came out. With a sufficiently large LO signal, it is a double balanced switching modulator with gain. A 1495 is a multiplier, and unusable for RF.

Tam

Reply to
Tam/WB2TT

I understand what you are saying, but I still do not agree with the relationship you are making between the linear system and an RF mixer. You do the math:

Here is a link to a discussion of linear system theory:

formatting link

And here is a link to mixer theory. Page down to Multiplication:

formatting link

Note that the linear system, at it's output, does not contain the product signals of the RF mixer at it's output.

There needs to be, and probably is somewhere, a definition of the in:out linearity that does not call a RF mixer linear.

Don

Reply to
Don Bowey

See my answer to John Woodgate. You're confusing time varying (which a mixer is) with nonlinear (which, ideally, a mixer isn't). If you wanted to convince me that a mixer must be linear _throughout_ you'd meet stiff resistance -- that just ain't true. But a mixer can be as linear at the terminals as just about any other device that uses semiconductors.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Reply to
Tim Wescott

I read in sci.electronics.design that Tim Wescott wrote (in ) about 'Multiplier VS. mixer', on Fri, 23 Sep 2005:

This can only apply to some particular sort of mixer that you have in mind. Surely it doesn't apply to a double-balanced mixer, which produces no output at the LO port due to an input at the signal port?

--
Regards, John Woodgate, OOO - Own Opinions Only.
If everything has been designed, a god designed evolution by natural selection.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
Reply to
John Woodgate

In this case the nomenclature is "h processes x...". The term "impulse response" not only doesn't define a nonlinear system, it often doesn't mean crap for a nonlinear system. So one does not use impulse response notation for general systems, only systems that are known (or stated) to be linear.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Reply to
Tim Wescott

Someplace along the line it should be ponted out that the output of a mixer only appears linear after the appropriate filtering. Look at it before band limiting, and it looks like crap.

Tam

Reply to
Tam/WB2TT

In a linear system, the impulse response cannot depend on the input itself. h cannot be a function of x.

Same for a time-invariant system. The impulse response cannot depend on the input itself. h cannot be a function of x.

Reply to
Mochuelo

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.