The correct answer is:
(a) Frequency doubler
Explanation:
A frequency doubler is a circuit specifically designed to double the frequency of an input signal. This circuit typically uses non-linear components, such as diodes or special configurations of operational amplifiers (op-amps), to generate a harmonic of the input signal, thereby doubling its frequency.
How it works:
- The input signal is processed through a circuit that generates a second harmonic (2f), which results in an output signal with twice the frequency of the input.
Why Other Options Are Incorrect:
- (b) Square doubler: A square wave itself can be used to generate higher harmonics, but this term does not specifically refer to a circuit that doubles the frequency of an arbitrary input signal.
- (c) Double multiplier: This term is vague and not commonly used to describe a circuit that doubles the frequency. It could refer to various other types of multipliers, but not specifically frequency doubling.
- (d) All of the mentioned: Since only a frequency doubler directly refers to frequency doubling, this option is incorrect.
Thus, a frequency doubler is the most accurate and commonly used circuit to double the frequency of a signal.