Analysis of three functions of capacitors applied to signal circuits

Difficult Problems:

What are the three functions of capacitors used in signal circuits?

Capacitors are used in signal circuits to perform coupling, oscillation/synchronization, and time constants:

1) Coupling

For example, the emitter of a transistor amplifier has a self-biasing resistor, which at the same time causes the voltage drop of the signal to be fed back to the input to form an input-output signal coupling. This resistor is the component that produces the coupling. Parallel connection of a capacitor, because the capacitor of the appropriate capacity has a small impedance to the AC signal, thus reducing the coupling effect caused by the resistor, so the capacitor is called a decoupling capacitor.

2) Oscillation / synchronization

Load capacitors including RC, LC oscillators and crystals fall into this category.

3) Time constant

This is the common integration circuit of R and C connected in series. When the input signal voltage is applied to the input, the voltage across the capacitor (C) gradually rises. The charging current decreases as the voltage rises. The characteristics of the current through the resistor (R) and capacitor (C) are described by the following formula:

i = (V/R)e-(t/CR)