±1V differential, ±50V common mode

[Smillsey]

Hi all

I am somewhat going round in circles here...

I need to design a differential measurement circuit to measure the voltage drop across a coaxial shunt which will have a frequency range of up to 10MHz.

Voltage across the shunt will be +/1V max (at lower frequency)

The common mode can be up to +/-50V

I was thinking about a differential amp based on the LT5400 and 3x ADA4817.

My rails will be +/-5V to the op amps

The shunt resistance is 10mOhms

I tried to simulate a 3 op amp instrumentation amplifier which failed - I will upload it shortly.

I want a 10V/V gain on this part of the circuit.

I tried to simulate a modified version of the ADA4817 datasheet, see attached.

But I just have an oscillator so i am missing something pretty obvious.... Any ideas?

 

[Smillsey]

We will all be very interested to to see the ckt you decide on .....

Sure I will post up the finals schematic

I’ll have a trimmed differential front end to bring the common mode within the limits of the ADA4817, then a differential amplifier stage.

The ADA4817 datasheet is pretty good at giving guidance on keeping the loop stable so should be ok there.

I’m using about 15 ADA4817-2 in this product