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Differential Amplifier with high impedance of the Vref input

Nir Porat
Intellectual 590 points
Other Parts Discussed in Thread: INA148, INA326, OPA317, INA331, INA332

Hello,

I am looking for differential amplifier with vref and high input resistance at the Vref input (would like to use resistors to set the voltage with minimal current )

can you suggest any amp?

  • 0
    TI__Mastermind 25775 points

    Hello Nir,

    To directly answer you question, please look at the INA148.  However, note that using a resistor divider to provide the reference voltage imbalances the integrated precision trimmed thereby reducing the CMRR performance of the device (and all other difference amplifiers). 

    Perhaps you should consider an instrumentation amplifier.  One unique IA is the INA326, whose topology allows for the use of a resistor divider to set the reference voltage (see Figure 6 of the INA326 data sheet).  Please note, however, that it is a 5V device whose input common-mode voltage is (V-)-20mV to (V+)+100mV.  Therefore this device will not work if you have an input common-mode voltage far beyond the power supply.  

  • 0 in reply to Pete%20Semig
    Intellectual 590 points
    Actually i need to amplify signal from stain Gage which is winston bridge.
    and i would like to use 10-20K Ohm resistors for vref offset,
    will this model may fit?
    Is there any low cost solution ?
  • 0 in reply to Nir Porat
    TI__Mastermind 25775 points
    Hello Nir,

    Assuming the common-mode voltage of your Wheatstone bridge is near mid-supply (e.g. 2.5V with a 5V supply), you can use an instrumentation amplifier. You could use the INA326 in such a configuration (assuming a 5V single supply). Concerning the magnitude of the resistors, I would prioritize the selection of the amplifier over the magnitude of the discrete resistors. In other words, I would design around the INA326 instead of the 10-20kohm resistors.

    For a lower cost solution, you could potentially use the INA331 or INA332. However, those devices require an external op amp to buffer the reference voltage. A low-cost precision amplifier that you could use is the OPA317. The total system cost of the discrete solution is then less than that of the INA326 solution at the expense of PCB space and accuracy.
  • 0 in reply to Pete%20Semig
    Intellectual 590 points

    Hey,

    Thank you for your replay,

    However i do have space limitation ,

    I have tried also INA 331/332, it seems to work, but too noisy,

    do you have any other one product solution , low cost and smaller?

    My bride is a strain gauge.

    I am using 3V for the input.

     

  • 0 in reply to Nir Porat
    TI__Mastermind 25775 points
    Hello Nir,
    The INA326 is the only difference/instrumentation amplifier that can utilize an un-buffered resistor divider reference voltage without introducing significant error.