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The OPA2810 datasheet mentions:

An additional advantage of configuring an amplifier for single-supply operation is that the effects of PSRR are minimized because the low-supply rail is grounded.

This description is unclear.

I guess this is because a split supply (+/-Vs) introduces not only +Vs noise, but also -Vs noise.

If I configure an amplifier for single supply, then only +Vs noise can be introduced. Because -Vs = GND (approaching 0), noise also approaches 0.

Is this right?

ocrdu
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curlywei
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  • (The wording "effects of PowerSupply[variability]RejectionRatio" is a bit off: PSRR does not have any effect on its own.) – greybeard Apr 03 '23 at 07:42

2 Answers2

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Kind of right, kind of wrong:

When you say "noise", you always mean "a measure relative to something", and that "something" is ground.

So, there's nothing "approaching" about that, there actually is 0 noise between GND and GND, by definition.

Marcus Müller
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    That definition does not allow for ground loop effects. I work quite a bit with amps and have a 380kV line in a quarter mile of distance. It actually takes a lot of effort to make sure to match the amount of noise between GND and GND to that in the related signal path or otherwise compensate for it. – user107063 Apr 03 '23 at 20:16
  • @user107063 ah well, I of course meant very local measurements. – Marcus Müller Apr 04 '23 at 05:26
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An additional advantage of configuring an amplifier for single-supply operation is that the effects of PSRR are minimized because the low-supply rail is grounded.

That only applies if the input and output is ground-referenced. That's often the case, but not always the case.

For applications where PSRR and CMRR are limiting, bootstrapping the op-amp's power supplies to the input common mode helps with both, but adds circuitry. Bootstrap is used most often in precision DC circuits, where CMRR unduly affects linearity, and in high-impedance input circuits, where the effective input capacitance has to be kept to a minimum.

In a circuit where PSRR is a primary concern, one can add either point-of-load regulation or filtering, or bootstrap. Both will have a similar effect, since bootstrap voltages are meant to be "clean".

Kuba hasn't forgotten Monica
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