OPA365: OPA365

Part Number: OPA365

I am trying to use the OPA365 as an inverting amplifier for the signal from this contact microphone sensor: http://www.mouser.com/ds/2/418/Contact_Microphone-769347.pdf . However the DC bias that I apply to the + input pin(1.65V) of the amplifier doesn't bias the output signal properly and there seems to be some sort of temporal response. The output signal ends being biased at 500mV after a while. Additionally this DC bias varies when I assemble the same circuit with a different OPA365 chip. This behaviour is quite unpredictable and I would appreciate if anyone could suggest a solution or if I am using the wrong amplifier for this application please let me know another that might be better suited for used with this sensor.

Thanks

3 Replies

  • Hi Zain,

    Would it be possible for you could to attach your circuit of inverting amplifier configuration using the OPA365 to help debug your issue?

    Best Regards,
    Rohit
  • In reply to Rohit Bhat:

    Hi Rohit,

    Here is the TINA schematic here we are using. We want to ensure that we can use this amplifier (or another amplifier from TI you can suggest for this application) to reliably amplify and buffer the sensor linked in the above post. The simulation in TINA is working appropriately however when we assemble the circuit in the lab with the actual sensor it doesn't behave correctly and consistently. The output DC bias doesn't go to 1.65V and it seems to change over time for some of our trials. Are we simulating wrong or not using the correct amplifier for this sensor? 

     Thanks

  • In reply to Zain Hasan:

    Hi Zain,

    It looks like the OPA365 circuit configuration you have attached might be oscillating with the selected Rf and Rg values. This could be a reason as to why the DC bias point at the output is not stable. I would recommend you to reduce these values to a more reasonable 49k and 5k for Rf and Rg, respectively. Comparing the TINA-TI simulation for both circuits gives lesser peaking and more stable circuit for the lower value Rf and Rg resistors. As such, the OPA365 should be a good part to use in microphone sensing application.

    Best Regards,

    Rohit