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TIPD181: Microphone Signal is not amplified

Jejomar Ildefonso
Expert 8890 points
Part Number: TIPD181
Other Parts Discussed in Thread: OPA172, TINA-TI

Hi Team,

I want to rebuild the TIPD181 pre-amplifier. My first step was to order the TIDC916 PCB from JLCPCB. Then I assembled all parts from the TIPD181 reference design guide.

I applied a voltage of 9 V and measured at the highlighted spots of the schematic to GND. The color of the arrows matches the corresponding waveforms.

All measurements were done in AC mode (x: 100ms/div, y: 10mV/div).

The microphone signal (darkblue) seems to be fine. But the signal is gone after the capacitor C3 (lightblue).

The output signal of OPA172 (orange) is about 0 mV and not the amplified input signal. It is the same at the RCA connector (yellow).

After this I found “TINA-TI Reference Design Companion for TIA Microphone Amplifier Circuit” which confused me even more. The file (SBOA291.TSC) contains a similar circuit. A transient simulation (image below) tells me that the input signal (± 2,83 V) is lower than the output signal (± 1,70 V).

How do I amplify the microphone signal? Why is the input signal smaller than the output signal in the simulation?

I built this design now three times. It is always the same result.




Kind Regards,

Jejomar

  • 0
    TI__Mastermind 23310 points

    Hi Jejomar,

    How are you stimulating the electret microphone? The input signal looks to be picking up some low frequency signals. Would you be able to stimulate it using a 1kHz sine wave or something that would be easy to see on an oscilloscope? 

    Jejomar Ildefonso said:
    How do I amplify the microphone signal? Why is the input signal smaller than the output signal in the simulation?

    I think the input is a little misleading here. The document explains this as a way to represent the SPL (in pascals) of the input signal to the microphone. The input of this isn't the output of the electret microphone, which would be represented by current rather than voltage. The input shown is the stimulus into the microphone. So this isn't showing that the input is larger than the output signal since the input is SPL being represented in TINA as a voltage signal.

    Definitely a little confusing! But hope my explanation clears up a few things. 

    Best Regards,

    Robert Clifton 

  • +1 in reply to Robert Clifton56
    TI__Expert 8890 points

    Hi Robert,

    Thanks for looking into this. I just found the problem. Unfortunately I used a OPA172IDCKT with SC70-5 footprint. But the reference design is built for OPA172IDBVR with SOT-23-5 footprint. Only V- and V+ are at the same location at these footprints.

    We can now close this issue. Thanks for your help!


    Kind Regards,

    Jejomar

  • +1 in reply to Jejomar Ildefonso
    TI__Mastermind 23310 points

    Hi Jejomar,

    The different pinouts would definitely cause a major problem! I'm glad I was able to help you better understand the system. Let us know if you run into any other problems or have additional questions!

    Best Regards,

    Robert Clifton