LT1167 Instrumentation Amplifier Gain

Discussion in 'General Electronics Chat' started by Dritech, Feb 15, 2016.

  1. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
    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,
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,050
    3,244
    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.
     
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  3. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
    2,503
    380
    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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