Question

Coherent demodulation of FSK signal can be detected using

• A. discriminator detection
• B. bandpass filter and envelope detectors
• C. matched filter
• D. correlation receiver

Hint:

Coherent detection almost always involves correlation. The receiver "correlates" the incoming signal with perfect local copies of the possible transmitted signals to find the best match.

Answer 1

The Correct Option is D

Step 1: Distinguish Coherent and Non-coherent Demodulation.

Non-coherent detection doesn't need a phase-synchronized local carrier. Examples are envelope detectors (for ASK) or discriminators (for FSK).
Coherent detection needs a local reference signal phase-locked to the received carrier, offering better noise performance.

Step 2: Analyze the options.

(A) Discriminator detection: A non-coherent FSK method that measures instantaneous frequency.
(B) Bandpass filter and envelope detectors: A typical non-coherent FSK receiver.
(C) Matched filter: The optimal linear filter for maximizing SNR, often part of a larger receiver. While used in coherent systems, "correlation receiver" better describes the coherent FSK demodulator.
(D) Correlation receiver (or correlator): The standard structure for a coherent detector. It correlates the incoming signal with synchronized replicas of possible transmitted signals (e.g., one for frequency \(f_1\) and one for \(f_2\)) and integrates the result. The path with the larger output indicates the detected bit, defining coherent FSK detection.