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TLV320ADC6140: Differential Inputs

Sean Heffernan1
Intellectual 290 points

Part Number: TLV320ADC6140
Other Parts Discussed in Thread: THS4520,

I'm using a THS4520 circuit to drive a differential signal into the ADC. Should the differential inputs be AC coupled, in order to avoid any common mode voltage issues?

  • 0
    TI__Guru 65055 points

    Hi Sean,

    Yes, AC couple the inputs to the ADC.  You can set the capacitance based on the 10k/2.5k input impedance settings.  The device can operate with DC coupled inputs, but you'll need to set the VOCM voltage to the ADC input common-mode voltage.  Also, in DC coupled mode, the performance is degraded by roughly 1dB.

  • 0 in reply to Collin Wells
    Intellectual 290 points

    Thanks Collin.

    The TLV320ADC6140 datasheet says that it supports a differential full-scale input of 2Vrms when AVDD = 3.3V. By my calculation, this is equivalent to a differential input of 5.66Vpp. So does that mean that each of the two differential inputs will see a 2.83Vpp signal?

    I'm AC-coupling the inputs, so can I set the Vocm of the THS4520 to GND and drive a +/-1.415V signal into each of the coupling capacitors?

    Sean

  • 0 in reply to Sean Heffernan1
    TI__Guru 65055 points

    Hi Sean,

    Yes, for a full-scale reading, the inputs will be driven with two 180 degree out of phase ~2.8Vpp signals.

    Yes, this will work provided you're powering the THS4520 in a manner that allows for a GND connected VOCM.  

      

  • 0 in reply to Collin Wells
    Intellectual 290 points

    Collin,

    Yes, we are powering the THS4520 with +/-2.5V. So it sounds like this configuration will work well. Thank you