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VGA for 10 to 15MHz (DC or AC) Signal for ADC input

Question asked by chrisrock on Mar 13, 2015
Latest reply on Mar 20, 2015 by JinoL

Hi,

 

I'm looking for a VGA circuit, which is capable to amplify and attenuate input voltages from 10mVpp to 7Vpp. This is needed to

bring the signal level to ADC input level, 1Vpp differential.

The VGA input signal is from a coil to measure the fieldstrength.

 

At the moment, I'm using following:

Coil -> 10:1 scope probe -> (1MOhm input) OpAmp follower -> AD8370 -> ADC

 

OpAmp is used as impedance converter.

The AD8370 is used as shown in Figure 51 in the datasheet.

 

For high voltages it works nice, but when it goes down to 40mVpp the AD8370 starts to swing at higher gains in high gain mode.

I build the circuit on a breadboard. That might be the problem.

 

Which VGA is the best for this problem, or is the AD8370 the best for that?

Other solutions, ideas?

 

Thanks!

KR

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