Direct Current and Capacitive Coupling - an overview

The transfer of energy within an electrical network can be accomplished by means of displacement current between circuits.The effect can be intentional or accidental.

In its simplest implementation, aCapacitor is placed between two nodes.In a matrix form, the capacitance at each point and between points can be described.

The AC signal from the first circuit can be used to connect the next circuit if DC is blocked.The two coupled circuits have DC bias settings.The capacitor used for the purpose is also known as a DC-blockingCapacitor.

The ability to prevent a DC load from interfering with an AC source is particularly useful in Class A amplifier circuits.

The low Frequency gain of a system is decreased by the use of Capacitive Coupling.A cumulative filter with a 3dB frequency may be higher than the individual filters if the next stage has a high-pass filter along with the input electrical impedance.Capacitors used for low frequencies must have high ratings.At the lowest frequencies of interest, the reactance of each should be at most a tenth of the input impedance.See the Impedance Bridging.

Capacitors can introduce distortion at low frequencies.It's not an issue at high frequencies because the voltage is very close to zero.If a signal is allowed to pass through the coupling that is low relative to the RC cutoff frequencies, it can cause a change in the capacitance of theCapacitor, which can lead to distortion.By using large values that put the cutoff frequencies far lower than the frequencies of the signal, this is avoided.[2][3]

The disadvantages of DC-biased transistor amplifier circuits are minimized in directly coupled designs.