A signal may have frequency components which lie in the range of 0.001 Hz to 10 Hz. Which one of the following types of couplings should be chosen in a multistage amplifier designed to amplify the signal?

To amplify the signal that has frequency components in 0 Hz to 20 Hz range via a multistage amplifier, the direct coupling method is best to couples the individual's amplifier.

Direct coupling is used in a multistage amplifier because it connects the output of one stage directly to the input of the next stage. (Option (2) is correct)

In multistage amplifier design, generally, three kinds of coupling are used:

1)  Resistor-capacitor (RC) coupling

2) Transformer coupling

3) Direct coupling

• RC coupling is generally used in audio-frequency range (ie. 20 Hz to 20 kHz) and not useful for low-frequency range because the coupling capacitor gets affected at low frequencies.
• Transformer coupling is used in power amplifiers i.e. higher frequency range and its frequency response is not good.

Important Points:

Comparison between different type of coupling method

Multi-stage amplifier is cascade connected individual amplifiers which provide desired gain, power and full-fill all the requirement of an ideal amplifier.

Example: Cascade amplifier, Darlington-Amplifier.