I'm having problems understanding this exercise:
The question asks that I find the "oscillation conditions" (which I assume is the value of \$K\$) as well as the frequency of the oscillation for C = 100 nF and R = 1 kΩ.
The approach I used for the problem was based off of other course examples:
The circuit consists of 3 op-amps in the inverting configuration.
Op-amps 1 & 2 have a transfer function $$ H(s) = -\frac{1}{sRC} $$ each. Op-amp 3's TF is $$ H(s) = -K $$. Together their TF should be $$ H(s) = -K\frac{1}{(sRC)^2} $$ which is always a positive real number.
My issue is that when I try to apply the Barkhausen criterion where \$ \arg(H(s)) = 0 \$ -- it always applies regardless of frequency. If that's true (which I suspect it isn't) then what frequency does it oscillate at?
I think I've either missed something (and I'm going to be feeling very silly for asking) or I just don't understand the oscillators properly.
The question doesn't specify, so I must assume all op-amps are ideal.