AnsweredAssumed Answered

Next step in frequency response beyond AD8429

Question asked by bryan80 on Jun 21, 2012
Latest reply on Jul 1, 2012 by bryan80

Hello,

 

I'm trying to measure a ~50mV differential voltage output from a Wheatstone bridge. The common mode voltage is around 7.5V due to the supply voltage of 15V. I am looking for a gain of 20-30 in order to obtain good signal strength for an Oscilloscope measurement, without sacrificing bandwidth. My application needs a flat response out to about 1-3 MHz, whereas the high bandwidth monolithic instrumentation amplifiers, such as http://www.analog.com/static/imported-files/data_sheets/AD8429.pdf, have a 3dB bandwidth near 3 MHz for gains of 10+ (not flat out to 1-3 MHz region).

 

My question is, what is preventing me from using an ultra-fast op-amp, such as http://www.analog.com/en/high-speed-op-amps/current-feedback-amplifiers/ad8003/products/product.html, and arranging it in an instrumentation amplifier topology by adding trimmed resistors. The AD8003 even includes 3 op-amps in the package, which would be nice for in-amp design. I have read that a good rule of thumb is to have your measuring device capable of measuring 20-30x the frequency you wish to measure in order to ensure good measurement capability.

 

I know there are other factors at play: picking up ambient high frequency signals, PCB layout and shielding layers to ensure correct functionality, etc. and it does seem that the AD8003 might be overkill, but I know there must be a basic limitation that I am overlooking and am essentially asking you all to point out my oversight.

 

Or, if you know of a good high-speed monolithic instrumentation amplifier or different amplifier topology that I should be pursuing, that would be great too.

 

Thanks!

Outcomes