When I googled Miller integrator the sixth picture that popped up is this one, but I'm not completely sure what circuit it is and if it is something similar to the simple "standard" op-amp Miller integrator? How is it different? (and HOW different are the two? If that question makes sense. ) The picture leads to the circuit implemented in CircuitLab, and the simulations I have done indicate that it does some kind of integration.

Circuit I found, which someone created in CircuitLab

This is not really my field, but the circuits are very important for my thesis in mathematics, and the circuit attached seems very interesting for what I'm working on (even more interesting than the normal op-amp integrator).

Is the circuit realistic? How does it behave, and why?

  • \$\begingroup\$ With an open loop gain of ten it barely constitutes an integrator. If your title is the only question (I see no other) then the answer is no to maybe to yes (depending on how tolerant you are on obtaining exact numerical integration). The term Miller Integrator is not really accurate either see this \$\endgroup\$
    – Andy aka
    Commented Feb 24, 2020 at 13:38
  • \$\begingroup\$ It would be a lot 'better' at integrating without R6 there, but then you'd need to alter the bias. A grounded emitter bipolar is very similar to an opamp in virtual ground configuration, with a lot less open loop gain, and an input offset. It depends what you want it to do, how integratey you need, whether it's any good. \$\endgroup\$
    – Neil_UK
    Commented Feb 24, 2020 at 13:53
  • \$\begingroup\$ For my analysis it does not matter what the circuit does, but I am looking for a realistic example, and wish to say what behavior one can expect. \$\endgroup\$ Commented Feb 24, 2020 at 14:31

2 Answers 2


Yes, that is a Miller integrator. But ...

Compared to an opamp. a 1-transistor common emitter amplifier has less gain, a higher input (equivalent) input bias current, and a higher output impedance. These combine for a circuit that is a less accurate integrator. That is, the integration time constant is not simply R4 x C1. To start with, the R for the time constant is the Thevenin equivalent of R1, R2, R3, and R4.

  • \$\begingroup\$ Ok, so there is an amplifying task performed by the NPN transistor and the way it is set up? Do you have some recommended site I can look up? Never heard about common emitter amplifier before, but sounds like I should check it out. \$\endgroup\$ Commented Feb 24, 2020 at 14:26

you may want vacuum tube examples as well. Old Tektronix manuals will have those.

And the TEK 556 oscilloscope has two internal sweep generators.


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