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High speed, high precision, low noise instrumentation amplifier?

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SheldonQ

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Hello, I need measure voltage difference between centr and shield coaxial cable (not groud).
Signal frequency 2MHz voltage 50uV - 100mV, amplifier gain 1x
So far, I consider the use of AD8620+AD8610 is a better option, or integrated instrumentation amplifier?
Or any other construction I can think of difference amplifier and Jfet Q as buffer for big input resistance or ...
 

Just for Analysis or design? A spectrum Analyzer would be far superior. Got one?
High impedance? Why? Ingres test?
Better to use BPF to reduce noise factor if possible.

Consider ADA4897-1: 1 nV/√HZ, LOW POWER, RAIL-TO-RAIL OUTPUT AMPLIFIERS
vs 6 nV/√HZ
 

ADA4897-1 is good idea, but my design work with +-12V power supply.
Signal is pure sinus symmetric around 0.
Impedance , I thing input current < ~20pA.
BFP can not be used (phase and time shift).
Any case, thank you for drawing attention to the new amplifier!
 

You didn't clearly tell about the intended pA bias current.

As far as I see there aren't much more JFET OP candidates than AD8620 (6nV/√HZ) and TI OP140 (5.1 nV/√HZ) for your application. Also discrete JFET amplifiers don't perform better.
 

Sorry , in current is typing error , real input current is below 20 nano Amper.

I''m sorry for the inconvenience
 

For high impedance, would current noise be dominant? If so, AD8620B is best.
. . . . . . ADA4897-1 . . . AD8620B

Offset µV Max . 100 . . . .300
Input Bias pA . . 10 . . . 130
nV/√Hz . . . . . . . 1 . . . . 6
fA/√Hz . . . . 2,800 . . . . 5
. . . . . . . . . . . . 2.8pA/√Hz
 
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It's not only noise current. ADA4897 is a bipolar OP with about 10 µA bias current.
 

Thanks you,
probably stay with AD8620, I have pledged ada4627, Unfortunately, Analog do not make ADA4627-2.
 

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