What is the circuit transfer function H(jω) defined as?

What is the circuit transfer function H(jω) defined as?

• A. Time-domain impulse response.
• B. Output divided by input.
• C. Input divided by output.
• D. The magnitude of the transfer function.

Answer: (B)

The transfer function in the frequency domain tells you how each frequency component of the input is scaled and shifted in phase by the circuit. For a linear time-invariant system, it is defined as the ratio of the output spectrum to the input spectrum: H(jω) = Y(jω)/X(jω). This means the transfer function represents the full complex response, containing both magnitude and phase information. The magnitude |H(jω)| gives the gain at each frequency, while the phase part describes the phase shift introduced. The time-domain impulse response h(t) is related to H(jω) as its inverse Fourier transform, so you can recover one from the other, but H(jω) itself is the frequency-domain ratio of output to input. The option describing the transfer function as the ratio of output to input is the correct one to capture this definition.