Question

How to design a basic amplitude-shift keying (ASK) demodulator circuit?

Answer 1

Designing a basic amplitude-shift keying (ASK) demodulator circuit involves converting the modulated ASK signal back to its original digital data. The ASK signal has two levels of amplitude representing binary data, usually 0 and 1. The demodulator circuit needs to detect these amplitude changes and convert them into digital logic levels. Here's a simple ASK demodulator circuit using an envelope detector:

Components required:

ASK modulated input signal
Capacitor (C1)
Resistor (R1)
Diode (D1)
Load resistor (R2)
Output buffer (optional)

Circuit diagram:

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           +------------------+   +-----+
ASK input--|     Capacitor    |-->|     |
           |       (C1)       |   |  D1 |-----> Demodulated output
           +---+-------+------+   |     |
               |       |          +-----+
               |       |
           +---+-------+-------+
           |   Resistor (R1)   |
           |                   |
           +---+------+--------+
               |      |
              _|_    _|_
              ///    ///
           Load resistor (R2)


Explanation:

The ASK modulated input signal is connected to the capacitor (C1) and the diode (D1).
The capacitor (C1) acts as an integrator and charges or discharges depending on the amplitude of the ASK input signal.
The diode (D1) rectifies the ASK signal, allowing only the positive half of the ASK signal to pass through.
The resistor (R1) is used to discharge the capacitor when there is no input signal.
The capacitor (C1) will charge and discharge depending on the amplitude of the ASK signal, resulting in a varying voltage across it.
The output of the demodulator is taken across the capacitor (C1).
A load resistor (R2) can be connected across the capacitor to discharge it slowly when there is no input signal, ensuring a smoother response to the incoming signal transitions.
Optionally, an output buffer can be used to isolate the demodulated output from the demodulator circuit.

Note: This is a simple envelope detector-based ASK demodulator and may not be suitable for all scenarios. In practical implementations, more complex demodulators may be used to handle noise, interference, and signal distortions better. Additionally, the choice of component values will depend on the specific ASK signal frequency and other application requirements.