Hello,
Just a question of pure theory . Why does the Miller's theorem not account for itself for the decreased output impedance when applying negative feedback ? To be clear :
suppose an inverting amp with a Rf / R feedback network with a gain of
- Rf/R. Rf is the feedback resistor joining the output to the inverting input ( = very classical !). Suppose also Zout to be the output impedance in open loop. Suppose Av is the gain in open loop. If we apply Miller's theorem on Rf it tells us that the effect on the output is equivalent to putting a resistor in parallel to the output that is worth = Rf * Av / ( Av -1 ) It does not account for the fact that Zout also decreases by a factor
1/ ( 1 + Av*beta).So I think that applying Miller's theorem in other conditions than calculating the parasite capacitors on the intput and output is misleading and even a trap.
What do you think of it ?
Friendly jptrol