Can I use Instrumentation Amplifier in this application?

Hey, I am currently in a situation where I have a DC output from LTC1968, and I would like to use some kind of op-amp (for example: instrumentation amplifier ) that can reduce noise and higher frequency. Below is the flowchart of the signal. My questions is:

1) Is there an instrumentation amplifier that can take one input signal (using +IN pin and probably grounding the -IN pin), since LTC1968 outputs a DC signal?  Note: I do not want to use an instrumentation amplifier that has dual output; a single output is preferred.

2) Beside instrumentation amplifier, do you have any other ideas. I can think of a low pass filter; is there even a higher order low pass filter? 

I hope to hear your response.



Edited for clarification
[edited by: shurp at 4:21 AM (GMT -5) on 16 Nov 2021]
  • +1
    •  Analog Employees 
    on Oct 27, 2021 2:32 AM

    Hi shurp,

    May I know what application are you trying to design? Can you elaborate what is the nature of your input? (Is it from an ac line or a sensor, voltage level, frequency, etc.) From your block diagram, may I know what is the purpose of your diff amp in the first block? Also is your system connecting to a converter after the InAmp stage here in the block diagram or does your microcontroller have an internal converter already?

    You may want to check this article if any application circuit here matches your application: Instrumentation Circuitry Using RMS-to-DC Converters.

    Regards,

    Kristine

  •  I am trying to design a circuit that measures milliohm resistance (not using this on a power line). Looking at the flowchart, I have two signal from a Wheatstone bridge; this two signal are sine wave and goes to differential amplifier to produce an output. The differential output goes to LTC1968 which outputs a DC signal. I want to increase the voltage gain and reduce higher frequency present on the output of the LTC1968; therefore, I am looking for some type of instrumentation amplifier that takes a single input. I know that most instrumentation amplifier requires two input but I only have one input from LTC1968. The microcontroller I am using has an ADC converter which works fine. I hope you can help in finding suitable instrumentation amplifier.

  • I hope the respond below answers what you wanted to know. Please let me know if there is any type of instrumentation amplifier that works well.  

  • +1
    •  Analog Employees 
    on Nov 2, 2021 3:04 AM in reply to shurp

    Hi shurp,

    Could you share what is the amplitude of your input signal and what your operating frequency and required gain is? Also in your block diagram in the first stage, do you mean difference amplifier? differential amplifiers are usually used as ADC drivers. If you're using a Wheatstone bridge, usually In-Amps are used to cancel out the high common-mode voltage from the Wheatstone bridge although a difference amplifier would also make sense in your block diagram especially if the common-mode voltage exceeds supply level. Using In-Amps will also let you have a large gain and filtered signal due to the bandwidth limiting. If you like to filter out your signal more, you can add filters after the RMS to DC converter to simplify your circuit. I would recommend Wheatstone bridge > In-Amp > LTC1968 > Filter(optional) > ADC, but this will still depend if your specs would match this signal chain.

    You may want to check AD8422 as it's typical application circuit has a Wheatstone bridge. 

    It would be helpful for us to suggest a part for you if you can share in detail (with defined specs) the signal conditioning that you will be doing (example: Wheatstone bridge > in-amp (5Vin, 1kHz, G=10, etc.) > RMS to DC > filter (BW, etc.). If possible block per block explanation would be great!

    Regards,

    Kristine