# Quiescent supply current of Opamp RROPAMP

Hi, I am currently trying Qspice (switching from LTspice) and I like the new generic op-amp model.

I have also read the article discussing its ins and outs here.

The issue I am facing is that I don’t know how to control its supply current draw. Supply current is a pretty important parameter in low power scenarios. If the quiescent current or the RROPAMP would be ~zero than one could obviously just add a small structure in parallel to the opamp to model the supply current.

But the current RROPAMP actually generates much more quiescent current than I want, so I would have to add a negative current source or resistor in parallel, which my gut feeling tells me is not a good solution and will eventually cause trouble.

Can the quiescent current of the RROPAMP be controlled by some of its parameters?

Small demo circuit below (attached here), showing 14 mA of quiescent current in my TLV9302 mock-up which in reality has 100x smaller quiescent current (150 µA):

If you set VCROSS=1p instead of 0, can you reduce the Quiescent Current?
I am a bit lazy to build your circuit to test it.

I only performed test of VCROSS for MultGmAmp, I observed that setting VCROSS=0 is equivalent to set VCROSS=2m. If to force quiescent current to ~0A, I have to set VCROSS=1p, and not put a 0 in there.

Hi KSKelvin,

(sorry I am not allowed to upload my schematic file )

I played with the Vcross setting quite a bit and I can conclude that it does nothing whatsoever. The quiescent current is not changed with any value. This conclusion extends to the other parameters such as Iout, Rout…

For the time being, I do include a current source, forcing 13.85 mA back up to the positive rail. But as I mentioned it sounds like a bad solution.

What does affect the quiescent current is the supply voltage. Namely, the current is proportional to supply voltage. Halfing the voltage halves the current, so it is a resistive behavior (not very opampy…).

What I also noticed is the following. The quiescent current (blue, which is 14 mA at no load current) goes up even more in proportion with the absolute load current (red). The blue trace is only the current which does not appear at the load, i.e. which goes right through the two supply terminals:

I see… as the Quiescent Current and VCROSS are related in RRopAMP building block MultGmAmp (OTA), I didn’t expect it has no effect in RRopAMP.
Let see if other community member has experience in the RRopAMP.

I am now allowed to upload the schematic file. Here goes:

RROPAMP_quiescent_current.qsch (8.0 KB)

KSKelvin, I had a look at the MultGmAmp and I do know now, why the quiescent current arises.

If you have a look at this schematic below, you see that there is a direct resistive path from V+ to V- which is given by the Rout setting. In contrast to what I said earlier, the Rout definitely does change the quiescent current.

I also confirmed that Vcross, when set to 1p, does change the transition behavior, but the majority of the quiescent current comes from those resistors.

Now what to void this in the Opamp model? I could set Rout to much higher values, but if I do, won’t that change other behavior of the model ? Also, increasing Rout, will still leave the quiescent current of the MultGmAmp, which is also ~1.5 mA ;(

I investigated the quiescent current of the RROPAMP. The quiescent current is equal to the current of a 10k ohm resistor. I compensated it with a -10 kOhm resistor connected between the power supply pins.

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Just to clarify, you are referring to MultGmAmp or RRopAmp for quiescent current still at 1.5mA at +/-15V input?

Useful workaround. One could finally add back an active load with `Vsat` specced to simulate to supply current draw.

@Engelhardt As you advocate the RROPAMP as a general component so much (and I agree it is necessary), it should provide much better handling of the supply current. Especially because the supply current terminals are even used by some functional opamp circuits.

That comment was targeted at both I guess. I observed that 1.5 mA in both my tries with the RROPAMP and the MultGmAmp.

I need to clarify that as I can get quiescent current less than 1.5mA in MultGmAmp by the value of VCROSS.

OTA-Qcurrent.qsch (4.6 KB)