How could I choise the break point on the feedback loop of an oscillator (goal: evaluate the loop gain \$\beta \space A\$)? The Sedra-Smith said that it is convenient to break the feedback loop at the aplifier output. I found a case in which this not works: a phase-shift oscillator with an inverting amplifier. In this case, if a break the feedback loop at the amplifier output Vu, i obtain Vu=0 because the "+" terminal of op-amp is at 0V and hence the loop gain \$\beta \space A\$ is 0 (Vp is the voltage source on the opposite side of Vu):
$$\beta \space A=\frac{Vu}{Vp}=0$$
In figure there isn't inverting amplifier.
Thank you for your help.
