What's a good instrumentation op-amp?

Franklin

I am trying to get about 500 to 1000 gain in a low noise opamp,· probably 1khz or less. What should I be looking for?
Thanks

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- Stephen

kwinn

Check out the Op177 data sheet.

Tracy Allen

The LT1028 is a classic low noise bipolar op amp good up through audio frequencies. It is best for signal sources with low impedance, such as magnetic pickups. It has more than enough gain bandwidth (75 MHz), for a gain of 1000 at 1 kHz without distortion. It's voltage noise density is about 1 nV/rt Hz at 1 kHz, which is close to the Johnson noise of a 50 Ohm resistor at room temperature. However, it would not be good at all with a high impedance input, such a crystal pickup. Its input current noise is way higher than a good FET input op-amp.

Here is a comparison of a couple of Linear Tech op amps, one for low impedance sources and one for high impedance work

LT1028 (bipolar) GBW=75 MHz, e_n=1 nV/rtHz at 1 kHz, i_n= 1 pA/rtHz
LTC6244 (cmos) GBW=50 MHz, e_n=8 nV/rtHz at 1 kHz, i_n= 0.6 fA/rtHz
(nano: 10^-9) (pico: 10^-12) (femto: 10^-15) (rtHz: square root Hertz) (GBW: gain bandwidth)

Lots of specs define an op amp--That is why their data sheets are so long and confusing! Of course you have to clarify how low a noise your application really needs based on the signal source impedance and its intrinsic noise level. But you do probably need the GBW, 1 MHz certainly, better 10 or 20 MHz.

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Tracy Allen
www.emesystems.com