Hello All, I've run into a circuit that I'm simulating but the results are not what I expected. The circuit is a negative feedback op-amp circuit with a 100 Ohm resistor at the inverting input, a 100 Ohm resistor from the non-inverting input to ground (for bias currents probably) and a parallel resistor-capacitor in the feedback path (8.45kOhm and 47 pF, respectively). According to my calculations, the gain equation should be:
A = Rf/Rin( 1/ (1+j2*pi*f*Rf*C) )
Using the values Rin = 100 Ohm, Rf = 8.45kOhm and C = 47 pF, the cutoff frequencty (-3 dB) should be about 400 kHz.
When I run the simulation, the gain falls 3 dB at 12.4 kHz.
What am I forgetting?