Methods of coupling

Resistance-capacitance (RC) coupling

It is also known as capacitive coupling amplifier using this coupling are known as RC coupled amplifier the function RC coupling network is two-fold:

• To pass a signal from one to next
• To block the passage of dc voltage from one stage to next

Impedance coupling or inductive coupling

• It is also known as choke-capacitance coupling amplifiers using this coupling amplifier using this amplifier
  are known as impedance coupled amplifier, the impedance of the coupling coil depends on, Its inductance and Signal frequency.

Transformer coupling:

• Moreover, the secondary winding also provides a base return path; hence there is no need for a base resistance. Amplifiers using this coupling are called transformer-coupled amplifier.
• Direct coupling: this coupling is used where it is desirable to connect the load directly in series with the output terminal of the active circuit element.

Direct coupling is permissible only when:

• Dc component of the output does not disturb the normal operation of the load device.
• Device resistance is very low.