Automatic gain control

Hello! Does anybody have an idea of how to build an automatic gain control (AGC) circuit??? For exemple, amplify a signal (10mV signal or 20mV signal) to 5V. Regardless of what is in the input, the output should be

5V... something like this.... I appreciate any help! Anything will be helpful, a tutorial, a link, the circuit ! :-) Thanks a lot! Victor
Reply to
Victor hyppolito
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Audio, video, RF ?

Graham

Reply to
Eeyore

That=B4s for signal conditioning for strain gauges... My goal is to amplify a small signal (10mV, 20mV, 40mV) to 5V. But I don=B4t want to adjust the gain via a external resistor! I want it to be 5V regardless of the input signal.I get the signal from a wheatstone bridge... It doesn=B4t need to be THAT precise, it can be 4.5V, 4.6V.... Thanks for the reply! Victor

Eeyore escreveu:

Reply to
Victor hyppolito

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Please bottom post.

If it doesn\'t matter what your input signal is but you always want
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Reply to
John Fields

For what is essentially a DC signal the concept simply doesn't work !

How can the amplifier know the difference between a 10mV 10% output and a 10mV

100% output ????

Graham

Reply to
Eeyore

AGC loop adjusts gain until output is constant. AGC control voltage becomes the "signal".

I did this one time with a WWVB receiver... the stepping of the (coherent-style) AGC voltage was the recovered data.

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

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Can\'t you read?

That\'s not what the guy\'s asking for.  He wants to plug in a strain
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Reply to
John Fields

Yup. I know that. Not *quite* so severe in audio compressors but ......... :-)

I suppose you could have an AGC volts output then.

Don't think it helps any though.

Last time I checked, 'receivers' used ac signals ! Boom Boom !!! ;~)

Graham

Reply to
Eeyore

Some guys really worry me that they even think such a thing could be possible !

Graham

Reply to
Eeyore

10mV

Isn't "AC" just fast-moving DC ?:-)

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

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No.  DC stays on the same side of 0V.  AC crosses over.
Reply to
John Fields

be

10mV

:-)

LMAO ! I thought *I* invented that phrase !

Graham

Reply to
Eeyore

Sounds like you want a programmable gain amplifier, where you'll preset the gain to some known precise value. There are a variety of ways to do that, such as selecting feedback with a multiplexer.

Of course if you really just want 5V out regardless of the input you can simply use a 5V regulator and dispense with everything else. ;-)

Best regards, Spehro Pefhany

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"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
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Reply to
Spehro Pefhany

Bah ! Just change the reference voltage and its moving DC again ! ;~)

Graham

Reply to
Eeyore

I guess that puts you in the category of "doesn't have a clue." Sorry Charlie.

Reply to
Don Bowey

So you measure the feedback signal.

Don

Reply to
Don Bowey

Last time I checked receiver AGC was a DC signal.

Don

Reply to
Don Bowey

WWVB has two data transitions per second, so the AGC is two-level "DC"

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

Yep ;-)

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

be

The usual solution for something slow, like a strain gauge, is to use a two-quadrant multiplying digital-to-analog converter to control the gain.

I've got a circuit board in my desk drawer that used a Burr-Brown (now Texas Instruments) DAC7528 as the gain-controlling element. There are a couple of example circuits in the data sheet

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For faster circuits Anaolg Devices offer the AD600 and the AD602,

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I've used similar parts from Linear Technology (slower) and Burr-Brown, though I can't recall the opart numbers off the top of my head.

--=20 Bill Sloman, Nijmegen

Reply to
bill.sloman

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