LT1167 Instrumentation Amplifier Gain

Thread Starter

Dritech

Joined Sep 21, 2011
869
Hi all,

I am interested in using the LT1167 Instrumentation Amplifier (IA) to amplify a signal of few milliVolts. The datasheet states that the gain can be set with one external resistor to get gains of 1 to 10,000.
In many instrumentation amplifiers applications I see of the internet, I notice that they apply small gain to the Instrumentation Amplifier and then use a secondary op-amp to apply the remaining gain, Is there a reason for doing so?
I need a gain of 1000 but I am concerned that the higher the gain, the less the IA performance.

From the datasheet of the LT1167 I noticed the following:

Higher gain = higher nonlinearity
Higher gain = longer settling time
Higher gain = better CMRR
Higher gain = less bandwidth

Can someone please mention some advantages and disadvantages of increasing the IA gain?
Shell I apply the full gain or use a secondary op-amp?

Below is the link to the LT1167 datasheet:
http://cds.linear.com/docs/en/datasheet/1167fc.pdf

Thanks in advance,
 

crutschow

Joined Mar 14, 2008
25,267
Usually the reason for adding amplification at the output of the instrumentation amp is to improve the bandwidth for a given total gain.
If you don't need the bandwidth then you shouldn't need an additional gain stage.
 

ericgibbs

Joined Jan 29, 2010
10,487
hi Dri,
I use a 2nd OPA which has a rail2rail output voltage range.
The LT1167 has a output voltage limit of approx +/-1.2V less than the IA supply rails.
So for a IA circuit powered by say +/-5V that would have a +/-3.8V limit.

Also its possible to add extra noise filtering between the IA and the 2nd OPA.

E
 
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