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Amplifier using Time variable gain unable to amplify beyond certain limit

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jimmykk

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Hi Folks

I am using a variable gain amplifier AD605 and providing it a time variable gain as a ramp voltage(VGN) from 0 to 2.5V such that it will amplify the input 140mVpp within some milliseconds. But the problem here is that the input amplifies until a certain point and then it remains at that level thereafter without any further amplification observed as shown in the picture attached. I am not sure what's the reason behind this, is it the output range of the amplifier or any other reason. CAN ANYONE SUGGEST SOME USEFUL POINTS.



CHANNEL 1 INPUT AND CHANNEL2 OUTPUT
IMAGES TEK00189-192 SHOW THE PATTERN OF INCREASING OUTPUT AND TEK00202 IS THE IMAGE ZOOMED OUT IMAGE SHOWING NO CHANGE IN OUTPUT AFTER A CERTAIN LIMIT(CHANNEL2).
Datasheet AD605:-

http://www.analog.com/media/en/technical-documentation/data-sheets/AD605.pdf
 

FvM

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Clearly a case of output saturation.

Read the datasheet. Pay attention to maximum output voltage.
 

jimmykk

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Thanks FvM for your reply

I went through the data sheet but a bit unsure about what does this parameter Output Signal Range actually means. Can you please help me explaining this thing and how it causes amplifier to saturate coz i need to document it why it happens.

 

Audioguru

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I went through the data sheet but a bit unsure about what does this parameter Output Signal Range actually means. Can you please help me explaining this thing and how it causes amplifier to saturate
With a +5V supply its output can go down and saturate to 2.5V - 1.5V= +1V and it can go up and saturate to 2.5V + 1.5V= +4.0V when it has a 500 ohm load. Yours is a little better going down to about +0.75V and going up to about +4.25V.
 

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