Digital to Analog Modulation Techniques
Digital Signal — A digital signal is a signal that represents data as a sequence of discrete values; at any given time it can only take on one of a finite number of values.
Analog Signal — An analog signal is any continuous signal for which the time varying feature of the signal is a representation of some other time varying quantity i.e., analogous to another time varying signal.
- Digital-to-analog conversion is the process of changing one of the characteristics of an analog signal based on the information in digital data.
- A sine wave is defined by three characteristics: Amplitude, Frequency and Phase. There are three mechanisms for modulating digital data into an analog signal: ASK, FSK & PSK [Amplitude Shift Keying, Frequency Shift Keying & Phase Shift Keying].
ASK — Amplitude Shift Keying
- Amplitude Shift Keying is a technique in which carrier signal is analog and data to be modulated is digital. The amplitude of analog carrier signal is modified to reflect binary data.
Advantages
- It can be used to transmit digital data over optical fiber.
- It uses lesser bandwidth as compared to FSK thus it offers high bandwidth efficiency.
- The receiver and transmitter have a simple design which also makes it comparatively inexpensive.
Disadvantages
- It is susceptible to noise interference and entire transmissions could be lost due to this.
- It has lower power efficiency.
FSK — Frequency Shift Keying
- In this modulation the frequency of analog carrier signal is modified to reflect binary data.
Advantages
- Frequency shift keying modulated signal can help avoid the noise problems beset by ASK.
- It has lower chances of an error.
- It provides high signal to noise ratio.
- The transmitter and receiver implementations are simple for low data rate application.
Disadvantages
- It uses larger bandwidth as compared to ASK thus it offers less bandwidth efficiency.
- It has lower power efficiency.
PSK — Phase Shift Keying
- In this modulation the phase of the analog carrier signal is modified to reflect binary data. The amplitude and frequency of the carrier signal remains constant.
Advantages
- It is a more power efficient modulation technique as compared to ASK and FSK.
- It has lower chances of an error.
- It allows data to be carried along a communication signal much more efficiently as compared to FSK.
Disadvantages
- It offers low bandwidth efficiency.
- The detection and recovery algorithms of binary data is very complex.
- It is a non coherent reference signal.
In addition, there is a fourth (and better) mechanism that combines changing both the amplitude and phase, called quadrature amplitude modulation (QAM).
- Quadrature Amplitude Modulation, QAM is a form of modulation that is a combination of phase modulation and amplitude modulation.
So, these are the Digital to Analog modulation techniques and that’s how they works…
