Demodulation

Understanding Demodulation

• Demodulation refers to the process of extracting the original information-bearing signal from a modulated carrier wave. This is necessary for the content of the signal to be processed or used.
• Demodulation is the opposite of modulation and it happens at the receiving end in a communication system like radio, television, and telephone networks.
• The device that performs this extraction is called a demodulator.
• Demodulation is crucial for both analogue and digital communication systems, with the process slightly varying depending on the type of modulation used - whether it’s Amplitude Modulation (AM), Frequency Modulation (FM), or Phase Modulation (PM).

Types of Demodulation

Amplitude Demodulation (AM)

• Amplitude demodulation involves deducting the original message signal from an amplitude-modulated carrier wave.
• The most fundamental kind of AM demodulation is called envelope detection, which uses a simple diode to correct the polarity of the signal, followed by a low-pass filter to eliminate radio frequency components.
• This type of demodulation is susceptible to noise as noise can easily alter the amplitude of the signal, thus changes the outcome.

Frequency Demodulation (FM)

• Frequency demodulation is the process of recovering original signal from frequency-modulated signals.
• The simplest method of FM demodulation is slope detection, which relies on a tuned circuit with a response that changes its resonance frequency with respect to the carrier.
• Given that FM is less susceptible to noise, this type of demodulation usually yields better results than AM demodulation.

Other Important Concepts

• Just like modulation, demodulation also has a key parameter, termed as the demodulation factor, which essentially is the efficiency of a demodulator.
• Overdemodulation happens when the modulation factor extends beyond its maximum limit, leading to distortion of the demodulated signal.
• The types of demodulators include: simple diode detectors, ratio detectors, phase-locked loops (PLL), quadrature detectors, and others.
• Coherent demodulation is a technique where the carrier is in phase with the transmitter’s carrier, using phase-locked loops or other methods. This generally provides better performance but is more complex to implement.
• Non-coherent demodulation does not require a carrier with a phase related to the transmitter’s carrier. It is simpler but provides lesser performance than coherent detection.
• Successful demodulation requires careful consideration of the input signal’s characteristics (carrier frequency, modulation type, etc.), as well as the necessary output specifications.