| Electronics > Beginners |
| Decoupling dilema |
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| paulca:
So I have a noisy power rail for an amplifier circuit which uses a virtual ground. When I place a large decoupling cap on the power rail the noise is removed from the power rail but deposited on the ground. The amplifier inputs are ground referenced and I still have noise output by the amplifier. Similarly if I don't decouple the power rail the power rail noise is present on the virtual ground and is amplified by the amplifier. What seems to work is to not decouple the power rail, but to only decouple the virtual ground. But it sounds fishy to me. How does one deal with this issue, or do I have some other issue? |
| Audioguru:
The virtual ground passes the noise. An amplifier is supposed to have good supply noise rejection. The virtual ground should feed a very low current like only to the (+) input of an opamp. Then the "half the supply voltage reference" can be simply two 100k resistors in series from the supply and a reasonable filter capacitor value like 22uF. Please post the schematic of the amplifier and how it is biased with a virtual ground. |
| madires:
In case you like to see the circuit and read the original thread: https://www.eevblog.com/forum/beginners/circuit-review/ |
| paulca:
--- Quote from: madires on April 19, 2018, 03:32:22 pm ---In case you like to see the circuit and read the original thread: https://www.eevblog.com/forum/beginners/circuit-review/ --- End quote --- Thanks. I recreated one channel of the circuit on a breadboard and was able to recreate the noise. I tried lots of things to remove the noise being amplified off the power rail, but the thing that was almost perfectly successful was removing C3 completely. |
| paulca:
--- Quote from: Audioguru on April 19, 2018, 03:21:04 pm ---The virtual ground passes the noise. An amplifier is supposed to have good supply noise rejection. The virtual ground should feed a very low current like only to the (+) input of an opamp. Then the "half the supply voltage reference" can be simply two 100k resistors in series from the supply and a reasonable filter capacitor value like 22uF. --- End quote --- What about the feedback divider? Ground or 1/2 Vcc VGround? |
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