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I'm looking for a buffer as I am going to fan out a VCM signal from an ADC to multiple ADC drivers.

    ADC VCM out: 0.95V 10mA
    ADC dr in  : 10Kohm x 3

Looking at the SN74LVC3G34, the datasheet mentions high and low a lot and a "Function/truth Table". This makes it sound like a schmitt trigger to me. Should I not be looking for a buffer?

If buffers are not what I think they are, is the solution to just pick a 3xop-amp IC and set them up as voltage followers?

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    \$\begingroup\$ the 3G34 is a buffer gate for logic, not for analogue signals. \$\endgroup\$
    – PlasmaHH
    Commented Sep 1, 2017 at 8:33
  • \$\begingroup\$ then I suppose my follow-up question is: what is the keyword for analog buffers? Say what is the product category at digikey for these devices? \$\endgroup\$
    – toxUP
    Commented Sep 1, 2017 at 10:45
  • \$\begingroup\$ The one containing buffer but not logic but probably analogue or linear or something in its name. \$\endgroup\$
    – PlasmaHH
    Commented Sep 1, 2017 at 10:49
  • \$\begingroup\$ I don't understand: What is VCM? What is ADC? (obviously not "analog to digital converter") so also: what is an ADC driver? \$\endgroup\$
    – Curd
    Commented Sep 1, 2017 at 13:43
  • \$\begingroup\$ VCM = voltage common mode. ADC = analog to digital converter. adc driver provides interfacing between signal source and the adc, i.e. single ended to differential conversion and possibly level shifting to VCM. \$\endgroup\$
    – toxUP
    Commented Sep 4, 2017 at 7:42

2 Answers 2

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As you suspect, analog buffers are really only op-amps wired up as voltage followers... like the ancient LM110.

As such, using an actual op-amp that more closely matches your needs is usually more appropriate.

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  • \$\begingroup\$ Thank you. Several helpful answers here, but this technically answers my question. \$\endgroup\$
    – toxUP
    Commented Sep 5, 2017 at 5:47
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ADC VCM out: 0.95V 10mA

Please post the ADC datasheet. If it is specified to output 10mA then it is likely that there is already an opamp to buffer VCM inside the ADC. Perhaps you need to add a capacitor, which should be explained in the datasheet too.

ADC dr in : 10Kohm x 3

I suppose the voltage across these 10k resistors will be less than 1V, thus the current drawn from VCM will be much below 10mA. Thus I'm not sure you actually need to add follower opamp... Providing a schematic would help.

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  • \$\begingroup\$ ADC3424. Can't find much info there myself concerning this. The drivers (ADA4950) have info about the VCM input, stating that a buffer might be necessary as "The input impedance of the VOCM pin is approximately 10 kΩ to a voltage of nominally midsupply ". What does this mean? \$\endgroup\$
    – toxUP
    Commented Sep 4, 2017 at 2:44
  • \$\begingroup\$ I'd say "10 kΩ to a voltage of nominally midsupply" means the opamps' VOCM pin draws a current of (Vocm - Vmisdupply)/10k. What are the ADA4950 supplies? The ADC looks like a buffered output with 10mA current capability according to datasheet. The application schematic adds a 100nF cap on VCM, for low HF impedance I assume. It should work fine without an extra buffer... \$\endgroup\$
    – bobflux
    Commented Sep 4, 2017 at 10:22

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