Pwm Signal

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pulse-width modulation include better energy efficiency (less dissipation) and better performance with nonlinear devices


PWM signal:


Duty cycle of a PWM signal. that period. Hence, PWM signals can be used directly in controlling a process, without having to demodulate it.

Advantages of pulse-width modulation include better energy efficiency (less dissipation) and better performance with nonlinear devices. For example, a device may stick at low speeds, due to Coulomb friction.

This can be avoided by using a PWM signal having amplitude that is sufficient to overcome friction, while maintaining the required average control signal, which might be very small.

In pulse-frequency modulation (PFM), as well, the carrier signal is a pulse sequence. In this method, the frequency of the pulses is changed in proportion to the value of the data signal, while keeping the pulse width constant. Pulse-frequency modulation has the advantages of ordinary frequency modulation. Additional advantages result due to the fact that electronic circuits (digital circuits in particular) can handle pulses very efficiently. Furthermore, pulse detection is not susceptible to noise because it involves distinguishing between the presence and absence of a pulse rather than accurate determination of the pulse amplitude (or width). Pulse frequency modulation may be used in place of pulse width modulation in most applications, with better results.

Another type of modulation is phase modulation (PM). In this method, the phase angle of the carrier signal is varied in proportion to the amplitude of the data signal.

Conversion of discrete (sampled) data into the digital (binary) form is also considered a form of modulation. In fact, this is termed pulse-code modulation (PCM). In this case each discrete data sample is represented by a binary number containing a fixed number of binary digits (bits). Since each digit in the binary number can take

only two values, 0 or 1, it can be represented by the absence or presence of a voltage pulse. Hence, each data

sample can be transmitted using a set of pulses. This is known as encoding.

At the receiver, the pulses have to be interpreted (or decoded) in order to determine the data value. As with any other pulse technique, PCM is quite immune to noise because decoding involves detection of the presence or absence of a pulse rather than determination of the exact magnitude of the pulse signal level. Also, since pulse amplitude is constant, long distance signal transmission (of this digital data) can be accomplished without the danger of signal weakening and associated distortion. Of course, there will be some error introduced by the digitization process itself, which is governed by the finite word size (or dynamic range) of the binary data element. This is known as the quantization error and is unavoidable in signal digitization.

In any type of signal modulation it is essential to preserve the algebraic sign of the modulating signal (data). Different types of modulators handle this in different ways. For example, in pulse-code modulation (PCM) an extra sign bit is added to represent the sign of the transmitted data sample. In amplitude modulation and frequency modulation, a phase-sensitive demodulator is used to extract the original (modulating) signal with the correct algebraic sign.