Looking for Information on the Miller Effect


Thread Starter

Max Bateman

Would someone be willing to help me better understand the Miller Effect? I've come across this multiple times in various textbooks, but it's poorly explained.

Anyone have a simple version to share? Links are appreciated.

Thank you.

- Max
Promise I won't share the link with you .... BUT the wiki link is actually pretty helpful. I can break it down (might be better).

The basic idea is that if you have a feedback element between the output and input of an inverting amplifier, the element looks smaller by roughly the magnitude of the gain of the amplifier.

The mechanism is simple. change the input voltage by ΔV. If the other side of the feedback impedance, Z, were at a fixed voltage, then the change in current into the input, ΔI, would be ΔI = ΔV/Z and so the incremental input impedance (due to the feedback element only) would be ΔV/ΔI=Z.

If the feedback impedance is a capacitor, then it looks like a capacitor that is (1+A) times as large.
Basically, the capacitance from the input to output (or the base-collector capacitance) provides negative feedback. This is proportional to the gain of the stage and the frequency of the signal (like an integrator).
Most inverting amplifiers have this. Sometimes it increases the effects on capacitances of the base to collector terminal.

It's proportional to the gain... and that is why it exists.