Inter-Stage Coupling Capacitor


Joined Aug 1, 2013
You don't say what you want the values to achieve. For example, if you want flat frequency response within the passband, then the R-C corner frequency should be at least one octave below the lowest frequency of interest. If you want a high-pass roll off to limit the output bandwidth, such as in a telecom application, then reducing the coupling or feedback capacitor size can achieve this.

In both cases, the equation above is the one to use. For the feedback cap CF, R is the sum of the stage 2 output impedance, the feedback resistor RF1, and the impedance at the Q1 emitter. For the coupling cap C13, R is the sum of the stage 1 output impedance and the stage 2 input impedance.