Single-Ended Amplifier after an In-Amp

Discussion in 'General Electronics Chat' started by lyto, Dec 8, 2015.

  1. lyto

    Thread Starter New Member

    Dec 8, 2015
    Hello alltogether,

    I am new at analog circuit design and want to amplify a differential voltage from a push-pull wheatstone brigde. I will use an Instrumentation Amplifier for this purpose. The differential signal has a high Bandwidth (3 MHz), so i can`t set a high gain in my In-Amp (lets say it will be 5 with 3 MHz Bandwidth), because the In-Amp-Bandwidth (BW) decreases with higher gain.
    Is it possible to use the gain of 5 and amplify the In-Amp-output-signal with a single ended OP-Amplifier with a higher Gain (so my overall gain is 5*(gain of OP-Amp))?
    Sry for my bad english.

    Thank you,
  2. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
    Yes. This is sometimes called a compound amplifier. When doing this pay attention to the DC offset at the output of the first amp because the second amp will increase this along with the signal you want. You might have to add an offset trim adjustment. Can you post your schematic?

  3. lyto

    Thread Starter New Member

    Dec 8, 2015
    Hey ak,

    Thank you for your answer. I posted one circuit i want to use (it is a circuit from Analog Devices: CN-0273 with a gain of 5 and a bandwidth of 35MHz). (later will try another circuit and use only a monolithic in-amp...maybe AD8421)

    In the posted circuit I have a sensor in wheatstone bridge and the CN-0273 circuit as an instrumentation amplifier. (I need to put the Vref of the second stage to ground..) I will have about 5 sensors and InAmps and each sensor will be amlified. After this stage, I want to make the average of these outputs (Vout). So I will amplify the Vout signal with the averager again. How can I add an offset trim adjustment. (With VREF?)
    Thank you

  4. lyto

    Thread Starter New Member

    Dec 8, 2015
    Somebody has some suggestions, tipps??
  5. Picbuster

    Well-Known Member

    Dec 2, 2013
    Mcp6n11 is complete instrumentation amp gain 2R's
    Feet the output into an analogue mux.
    Now you have to decide the density (bits) and define adc.
    Use pic and do your calculations.
    Values are floats should take a pic able to handle that.

    Better Alternative is; use mcp3551 connected via SPI
    one multichannel adc like ltc(2448) connected via SPI