Electronic – Op Amp Decoupling with a Virtual Ground

decoupling-capacitoroperational-amplifier

I'm designing a low-frequency op. amp. circuit that operates from a single 10V supply. I'm using a TLE2426 "rail-splitter" to generate a virtual ground, 5V above earth ground, which is used as a reference for the op. amps. Normally, if I had bipolar +5V and -5V supplies, I'd decouple the high and low inputs of the op. amp. to the earth ground. With a single-supply op. amp. design, I've heard to decouple straight from the high supply to the low supply. So, I have the following possibilities:

  • 2 capacitors: op. amp. high to virtual ground, op. amp. low to virtual ground
  • 1 capacitor: op. amp. high to op. amp. low
  • 3 capacitors: both of the previous options

In theory, the first option creates an equivalent of the second option with half the capacitance, so long as the trace impedances are low. I was hoping for a discussion on the pros/cons and if there is a definite recommended approach.

Best Answer

It depends on where the currents are flowing. In general, if current flows from the power supply rails (your +10V/0V) through the load resistor to your virtual ground, I'd use three capacitors, with the one across the 10V supply before the rail splitter and two equal capacitors from the +5 and -5 rails to the virtual ground.

From the datasheet figure, you might want to consider a dummy load resistor to improve the stability if power consumption isn't a big deal to you.

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