[sdiy] Is this a comparator?

[Derek Holzer]

There's a function I want to implement, but I don't know what to call it 
so I can't start researching the right circuit.

I'd like to compare an incoming voltage with a reference voltage, and 
only allow the incoming voltage to pass if it's above the reference 
voltage. I do not want to square the signal, I want to pass it unaltered 
so long as it's above the threshold of the reference voltage. When the 
incoming voltage is less than the reference, then the reference voltage 
would be passed (or none at all).

What is this function called? A comparator? A gate? It's not a logic 
function, since it doesn't deal with square waves. I imagine it's a 
simple op-amp trick...

thx + best,
d.
-- 
derek holzer ::: http://www.umatic.nl ::: http://blog.myspace.com/macumbista
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