# Inter-Stage Coupling Capacitor

#### newbie2019

Joined Apr 5, 2019
95
How would you compute the value of the inter-stage coupling capacitor?
range 20 Hz to 20Khz

C = 1 / 2πF?
Schematic Attached.

Thanks

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#### Jony130

Joined Feb 17, 2009
5,089
Try this one
C = 1/(2 * Π* F * (Rc1 + Rin2))

#### newbie2019

Joined Apr 5, 2019
95

#### newbie2019

Joined Apr 5, 2019
95
I should have asked how you would compute the value of the negative feedback loop
capacitor and its voltage as well.

#### AnalogKid

Joined Aug 1, 2013
8,226
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.

ak