Binary Amplitude Shift Keying (BASK) or On Off Keying (OOK) is one of the digital modulation techniques in which the amplitude of carrier is switched according to the binary data. This digital modulation scheme is used to transmit digital data over optical fiber, point to point military communication applications, etc. Binary 1 is represented by a short pulse of light and binary 0 by the absence of light. Amplitude Shift Keying modulation and demodulation processes are relatively inexpensive and easy to implement. The main disadvantage of ASK is that it is sensitive to atmospheric noise, distortions and propagation conditions. Here is the practical circuit diagram of amplitude shift keying modulator using CD4016 IC. CD4016 is a switching IC with four embedded switches.
Also Read: Binary Phase Shift Keying (BPSK) Modulation
Working of ASK circuit
- Sine wave can be obtained from a function generator or by using a RC phase shift oscillator.
- Two switches inside the quad analog switch CD 4016 are used in the circuit. When the enable input of one gate is at high, then the input will appear at the output.
- When the binary data is 1, sine wave is switched to output because the sine wave is connected to 1st switch and the binary data is applied to enable pin (13th pin) of 1st switch.
- When binary data is 0, the 1st switch is disabled and 2nd switch is enabled using NOT gate arrangement.
- The input of 2nd pin is grounded, hence we get 0V for binary 0.
- The output pins of both first and second switches are shorted and the output is taken from it. The block diagram is self explanatory.