Question

In which filter the output and input voltages are equal in amplitude for all frequencies?

(a) All-pass filter

(b) High pass filter

(c) Low pass filter

(d) All of the mentioned

The question was posed to me by my school principal while I was bunking the class.

The query is from Active Filters in portion Active Filters of Linear Integrated Circuits

Answer 1

The correct answer to this question is:

(a) All-pass filter

Explanation:

• All-pass filter: In an all-pass filter, the output and input voltages have equal amplitude across all frequencies, but their phases are shifted. This filter does not affect the signal's amplitude but only modifies its phase response. Therefore, the output and input voltages are always equal in amplitude, regardless of frequency.

Other Filters:

• High-pass filter: A high-pass filter allows high frequencies to pass through with little attenuation, but at low frequencies, the output signal is attenuated, so the input and output amplitudes are not equal for all frequencies.

• Low-pass filter: Similarly, a low-pass filter allows low frequencies to pass with minimal attenuation and attenuates higher frequencies. Thus, the input and output amplitudes are not equal for all frequencies.

Therefore, the correct filter where the output and input voltages are equal in amplitude for all frequencies is the all-pass filter.