Automatic gain control

Audio, video, RF ?

Graham

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:

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

Graham

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

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

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

Graham

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

...Jim Thompson

be

:-)

LMAO ! I thought *I* invented that phrase !

Graham

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

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

Graham

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

So you measure the feedback signal.

Don

Last time I checked receiver AGC was a DC signal.

Don

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

...Jim Thompson

Yep ;-)

...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

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

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