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PCM4202: Single-ended input to PCM4204

user5284639
Prodigy 40 points
Part Number: PCM4202
Other Parts Discussed in Thread: PCM4204

Hi,

In order to input a single-ended signal to PCM4204 with minimum space/component requirements, despite high performance, is it possible to use a single OpAmp  as specified in this design, biased by a buffered PCM4204 VCOM instead of Ref pin? Can ADC IN- be connected next to VCOM buffer?

https://www.ti.com/download/kbase/adc/adsssds2.htm

Do you provide such reference design for PCM4204?

Thanks,

  • 0
    TI__Mastermind 23050 points

    Hi,

    You can get away with driving the input single-ended in a pseudo-differential configuration by tying the VIN- pin to VCOM, just make sure that your VIN+ input is biased around the same VCOM voltage. You will see a 6dB degradation in SNR since you have half the full scale range now and may also see somewhat worse distortion performance since even order harmonics are no longer cancelled as effectively. There may be some error in your 0 voltage as well based on the DC offset between the inputs (largely from whatever the op amp circuitry adds). As long as you are willing to accept the impact to performance you can operate this way without any problems.

    Best,

    Zak

  • 0 in reply to Zak Kaye
    Prodigy 40 points

    Hi,

    Thanks, 

    Is this recommanded to  tie VIN- to VCOM before or after the buffer?

    Regards,

  • 0 in reply to user5284639
    TI__Mastermind 23050 points

    Hi,

    Definitely after the buffer. The VCOM pin is meant for biasing high impedance nodes like an op-amp input. It does not have the drive strength to directly bias the VIN- pin since these devices typically have a 3kOhm input impedance.

    Best,

    Zak