Can I use one voltage divider to bias multiple points in circuit?

Question

I have 4 nodes in my circuit that require virtual ground of half the power supply voltage. 2 of the nodes are just offset for input signal and other 2 are for op-amp biasing to virtual ground.

Can I use one voltage divider to provide offset for all these nodes? This would greatly reduce BOM and save PCB area(eliminating 6 resistors and some capacitors), but I am not sure if this can't cause some kind of issues?

There was similar question, but it was talking about one IC, in my circuit I have two separate input connections and two op-amps(though they are in same package).

Also maybe a better question would be in more generic form - can one use single voltage divider to bias several points(no matter how many) to virtual ground? I understand that in some circuits the resistance on the output of voltage divider will basically make no sense, but if I for example have 16 op amps that need to be biased - will it work?

Answer 1

It all depends on how you make that virtual ground and how you load it.

A virtual ground is just a DC voltage used as a reference voltage for (usually) opamp circuits. This can be used to prevent having to use a symmetrical supply like +5 V and -5 V. Instead we use 10 V and make an internal 5 V as a "virtual ground".

You can bias 16 (or more) opamp circuits from your virtual ground as long as you take care that your virtual ground is not influenced too much by the circuits connected.

If you use inverting opamp circuits and directly connect the virtual ground to the + input of the opamp, no current is drawn from it so you can bias many opamp circuits.

An inverting amplifier, here the + input is grounded but that can be a virtual ground as well:

If you do load the virtual ground with each circuit then you have to make sure the virtual ground can supply all those currents.

To prevent the circuits influencing each other you might want to filter (Resistor in series, capacitor to ground) each virtual ground but that increases your BOM.

Also it is not so much the DC biasing current as it is AC currents resulting from the signal being amplified which can cause problems with a shared virtual ground.

Answer 2

Yes, you can. However, I would recommend that you look up the total of the input (leakage) currents for your 4 inputs then make the potential divider current at least 50..100 times that value while exercising some realism.

For example, four inputs with input current of 10 uA each would lead me to a potential divider conducting between 2 and 5 mA.

You can also consider putting a small capacitor on your potential divider output to steady it against rail noise, such as 10 nF. The exact value depends on your divider resistor values.

Answer 3

2 or 3? You're probably ok.

"No matter how many" or 16? Probably not. Of course it depends on your biasing resistor values, and the bias current of your OpAmp. But each one will introduce a small error into your bias point which will change where your "virtual ground" is.