Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cornell!uw-beaver!fluke!strong
From: strong@tc.fluke.COM (Norm Strong)
Newsgroups: sci.electronics
Subject: Gain control
Message-ID: <6950@fluke.COM>
Date: 14 Feb 89 15:16:20 GMT
Sender: news@tc.fluke.COM
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Organization: John Fluke Mfg. Co., Inc., Everett, WA
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}Probably a simple question, but:

}I want to be able to control the gain of an opamp by an external control.
}Normally I would just put a potentiometer in the feedback loop of the
}amp but I want to be slick about this. I want the gain to be controlled
}by the number stored in a register (probably converted to an analog
}voltage or current in a D/A converter). How can I do this? Is there
}some sort of inexpensive, small "voltage-controlled resistor" or something
}that will do this for me?


What you want is a "multiplying DAC"  Put the reference input on the output of
the amp, and the output of the dac on the inverting input.  Now the gain will
be controlled entirely by the digital address.  Analog Devices makes several
CMOS DAC's of the type you want.
-- 

Norm   (strong@tc.fluke.com)


-- 

Norm   (strong@tc.fluke.com)