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TPA2037D1YFFEVM: Differential Input

Jerry Chu
Genius 4915 points
Part Number: TPA2037D1YFFEVM
Other Parts Discussed in Thread: TPA2037D1

Hi Expert,

I used the EVM to test the THD+N performance and got the below result.

New EVM, Gain=2 (Input 1Vrms, Output 2Vrms)

Change C1=C2=18.7Kohm, want to reduce the gain to 1.78. But got the below result.

The input source both are from AP, why the THD+N performance is difference? Thanks!

  • 0
    TI__Guru* 84915 points
    Hi, Jerry,

    The first THD+N graph that you attached is correct, it shows a THD+N behavior as mentioned in the datasheet.

    However, in the second one, it seems that the input signal is not correctly biased as recommended in the datasheet. As mentioned in Input Capacitors section ( www.ti.com/.../tpa2037d1.pdf ), you must ensure that the differential input is biased with the common-mode input. Otherwise, you could get the results that you mentioned and the signal performance may be affected. If the signal that you are using is not biased in this way, then the input capacitors will be required in the design.

    Best regards,
    Luis Fernando Rodríguez S.
  • 0 in reply to Luis Fernando Rodriguez S.
    Genius 4915 points
    Hi Luis,
    The test source is from AP2722, I measured the input signal is no bias voltage. Is it also impact the performance?
  • 0 in reply to Jerry Chu
    TI__Guru* 84915 points
    Hi, Jerry,

    Yes, the TPA2037D1 requires of this common-mode or bias voltage to work correctly. If the input capacitors are removed, the output performance may be affected as shown in your second picture.

    If your system cannot generate the bias voltage, I would recommend to place again the default EVM capacitors.

    Best regards,
    Luis Fernando Rodríguez S.