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PCM1804: Differential input with single ended driver

Jar Grb
Prodigy 30 points
Part Number: PCM1804
Other Parts Discussed in Thread: PCM1809

Tool/software:

Hi

I got single ended source.

Is any benefit to convert it to differential with front end op amps(datasheet recommended)? Or simply connect in- to analog source gnd via capacitor? 

It looks in a both way I will have common mode rejection. only difference if voltage swing with split on two inputs or applied fully to one.

  • 0
    TI__Mastermind 27330 points

    Hi,

    I will update thread by Monday

  • 0 in reply to Daveon Douglas
    Prodigy 30 points

    Thanks.

    Please find schematics for my question. I need to know difference in performance on ADC output. difference in S/N and etc.  I made a fast tests, but I can't see any difference.

  • 0 in reply to Jar Grb
    TI__Mastermind 27330 points

    Hi Jar, 

    The PCM1804 requires a fully differential input for optimal performance. This is because the internal modulator and analog front-end are designed to operate with balanced differential signals referenced around the common-mode voltage (VCOM)

    Note: 
    Feeding a single-ended signal directly to one input pin (e.g., AINL+) and grounding the other (AINL–) unbalances the input stage, resulting in:


    • Degraded THD+N, SNR, and CMRR performance.
    • Increased susceptibility to common-mode noise and power supply interference.
    • Improper signal swing around the expected common-mode level.
    • The input common-mode voltage (referenced to VREF) must be maintained on both pins for the internal differential modulator to function correctly

    In short, yes you should use the application circuit in Figure 44

  • 0 in reply to Daveon Douglas
    Prodigy 30 points

    Thanks for your answer.

    • Degraded THD+N, SNR, and CMRR performance.

    how much exactly? it mught be not significant for my project. 

     

  • 0 in reply to Jar Grb
    TI__Mastermind 27330 points

    Hi Jar,

    I don't have the characterized data for single-ended performance on PCM1804. However, operating in this manner for any fully-differential ADC results in measurable degradation in SNR/DR/THDN. For best results and guarantee of datasheet specification, I recommend following the datasheet..

    Or 

    Transitioning the design to a newer generation ADC that allows single-ended/differential and AC/DC coupled configurability of the input. PCM1809 and the PCM182(0/1/2) devices provide more flexibility at a low cost.