Use op-amp or in-amp to amplify sensor output?

Discussion in 'General Electronics Chat' started by tpny, May 10, 2012.

  1. tpny

    Thread Starter Member

    May 6, 2012
    216
    0
    Hi, I have a temperature sensor that outputs 0~1V. I'm wondering whether to use an op-amp IC (eg, ad820) or in-amp IC (eg, ad623) to amplify them to 0~5V for my adc. My circuit runs on 12V battery. So I'm considering these ic's because they are single-supply and can output 0~5V given a 12V supply.

    Q1) If I use the op-amp, I'm thinking about CMRR. Is there such a thing as CMRR if the op amp is configured to take only a single input? For example, is there CMRR taking place at the following follower?
    Code ( (Unknown Language)):
    1.  
    2.  
    3. [FONT=Lucida Console] Vin-------------- V-|\[/FONT]
    4. [FONT=Lucida Console]                     | >---feedback to V-[/FONT]
    5. [FONT=Lucida Console]               --- V+|/[/FONT]
    6. [FONT=Lucida Console]               |[/FONT]
    7. [FONT=Lucida Console]              GND[/FONT]
    8.  
    9.  
    10.  


    Q2) So in consideration for CMRR, I'm thinking I need to connect two lines to the op amp inputs:
    Code ( (Unknown Language)):
    1.  
    2.  
    3. [FONT=Lucida Console]Sensor: output(+)-------------- V-|\[/FONT]
    4. [FONT=Lucida Console]                                  | >---feedback to V-[/FONT]
    5. [FONT=Lucida Console]        output(-)-------------- V+|/[/FONT]
    6. [FONT=Lucida Console]                           |[/FONT]
    7. [FONT=Lucida Console]                           | [/FONT]
    8. [FONT=Lucida Console]                          GND[/FONT]
    9.  
    10.  
    11.  

    Will Vcm (or noise) on both lines show up at the op amp inputs (and get rejected) or will the noise on the bottom line short to ground first?


    Q3) Or should I use an in-amp? Is ad623 a good one?

    Thank you so much!!

    http://www.analog.com/static/imported-files/data_sheets/AD820.pdf
    http://www.oup.com/us/pdf/microcircuits/students/amps/ad623-analog.pdf
     
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