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INA332: Is this circuit correct?

Part Number: INA332
Other Parts Discussed in Thread: INA818

I am considering using the INA332 to amplify a 60 kHz sine wave. The INA332 will drive other op amps to increase the output level to 5 volts.

I have questions about the circuit I have attached. Can the two 10k resistors (R1 and R2) be eliminated? A 1.1 mH inductor will be connected across PL1 and will resonate at 60 kHz with C1, C2, and C3. C3 is currently shown as TBD but is approximately 150 pF.

The input signal will vary between 50 uV and 4 mV. Do I have the biasing correct to allow this input range to work?

Thank you.

  • I pasted image into post but it didn't show up. I will try attaching file.

  • Hi Ray,

    Please try the following circuit. I moved the 2.5V bias voltage in front of 10kOhm resistor. 

    /cfs-file/__key/communityserver-discussions-components-files/14/INA332-E2E-10192020.TSC

    If you have additional questions, please let us know. 

    Best,

    Raymond

  • Raymond,

    Thanks for the suggestion. I will order a couple of the parts and experiment.

    I still have two questions though. 

    1) Can I eliminate the two 10k resistors and still have the circuit work? Could you simulate the circuit without the resistors present?

    2) According to the data sheet the INA332 has a noise figure of 46 nV/√Hz at 1kHz. Do you think that will have much of an impact on the input signal when it is at the 100 uV level at 60 kHz?

    Ray

  • Hi Ray,

    1) Can I eliminate the two 10k resistors and still have the circuit work? Could you simulate the circuit without the resistors present?


    Generally, the input resistor can limit the input current to the inputs of instr. amplifier. I think that you have very low input signals, you may eliminate the 10k resistors. 

    2) According to the data sheet the INA332 has a noise figure of 46 nV/√Hz at 1kHz. Do you think that will have much of an impact on the input signal when it is at the 100 uV level at 60 kHz?

    yes, the input noise at 1kHz is approx. 46 nV/√Hz, and at 60kHz, it is approx. 35 nV/√Hz (assume this is broadband noise). If we assume 2MHz BW, then the BB input noise contribution is approx. 35 nV/√Hz*√2e6Hz or  49uVrms. I do not know your nominal input signal and design requirements, so I am unable to comment on the topic appropriately (it seems that it is a bit high for the 100uV level). But the noise model is built in this part and you can check it out for yourself. 

    In addition, we have other instr. amplifiers, if the above input noise does not meet the design requirements. 

    https://e2e.ti.com/support/amplifiers/f/14/t/818894

    /cfs-file/__key/communityserver-discussions-components-files/14/INA332-E2E-Noise-10202020.TSC

    Best,

    Raymond

  • Raymond,

    Thank you for the additional input and simulations. I will test the circuit with and without the resistors. I will have very low input signals so I think the circuit will be fine without the resistors.

    The noise figure has me somewhat concerned. I ordered a few INA332 parts. I also ordered a couple of INA818 as their noise figure is much better.

    Ray