I have designed a circuit with 5V single-supply op amps, but since the inputs to the circuit are AC, I need a biasing voltage to replace the ground node on the equivalent dual supply circuit. Without getting into unnecessary circuit details, this biasing voltage may need to sink or source up to 10 mA.
The circuit amplifies signals of around 2 MHz, and originally I had used a wide bandwidth voltage regulator (TI TPS71701) to generate this biasing voltage, but I found out the hard way that this regulator is unable to sink current.
I've also tried using another, non-wide-bandwidth regulator (Diodes Inc. AP2202K), which did appear to work, but its datasheet makes no mention of being able to sink current, so I don't intend on relying on an undocumented feature.
Also I've tried using a low speed (1 MHz GBW) op amp (TI LMV342) configured in unity gain buffer topology. Although it does appear to work in practice, SPICE simulations indicate that there should be large (100 mV+) output voltage swings when sourcing/sinking a few mA of current at 2 MHz, which is unacceptable in this circuit. These swings disappear when frequency is reduced to 2 kHz. Hence I'm a little hesitant to put this into mass production.
I'm looking for suggestions of other low-cost circuits capable of generating a 2 V reference from a 3 V or 5 V supply, and which have no problem sourcing and sinking currents up to 10 mA at 2 MHz with little loss of regulation.
EDIT: I tried adding a load resistor to the output of the TPS71701 regulator, such that the amplifier circuit is able to sink current through this resistor. This did work, but now I have a constant 10 mA load (and this is a battery powered device). Actually, when in use, this product draws on the order of 1 A, so 10 mA might not be so bad, but still, I'd feel better with a circuit without a vampire current draw.
Best Answer
EDIT: I didn't see OP's edit where he says he already tried this. Anyway I'll leave this answer up for future readers.
You are correct that most voltage references cannot both source and sink current. One option is to either use a shunt reference or to pre-load a series reference:
simulate this circuit – Schematic created using CircuitLab
In this circuit, normally the reference IC provides 13 mA to R1. If the actual load (connected at OUT) needs to source current, that current will flow through R1 and U1 will just reduce its output current. I've shown both a filter capacitor (C1) to maintain stability of the reference/regulator, and bypass capacitance (C2) to take up most of the switching current and maintain steady voltage at the load under transients.
However, pre-loading is fairly wasteful of power (about 26 mW burned in the pre-load resistor, plus the extra current through the series reference). Andd 10 mA is a lot to ask from a precision reference circuit.
But if ~50 mW doesn't bother you, and you don't need sub-1% accuracy, it should work okay and doens't cost much.