Pulse Modulation and 4 of its most Crucial Types

Hello everyone I hope that you all are doing good in your life and are having fun. Today we are back with another topic related to communication systems i.e Pulse Modulation. In this topic, we are going to learn all about pulse modulation, quantization of its types errors, Companding, and also about types of pulse modulation such as; PCM, DPCM, DM, and ADM.

What is Pulse Modulation

Pulse Modulation is a kind of modulation in which a continuous signal is a sample after a fixed interval time using a set of the pulse train. Its main purpose is to transmit narrowband analog signals for example radio frequency, voice signals, etc.

Types of Pulse Modulation

Pulse Amplitude Modulation

In Pulse amplitude modulation the amplitude of the regular space message signal is varied in proportion to the corresponding sample values of a continuous message signal. The PAM output signal traces the amplitude and the path of the original message signal. However, it is one of the simplest techniques of pulse modulation.

The PAM signal which samples at the Nyquist frequency is easily reconstructable by simply using a low pass filter. This low pass filter helps in restraining the high-frequency signals and thus avoids the aliasing error. The waveform of PAM is similar to the waveform that of a natural sampling.

Thus the waveform of a PAM is shown below;

Advantages

1. Encoding and Decoding is easy.
2. Lastly easy construction.

Disadvantage

1. The requirement of bandwidth for transmission is quite high.
2. Noise interference.
3. Lastly requirement of various transmission power.

Application

1. Graphic cards.
2. The connection between ethernet and broadband communication.
3. Radio stations.
4. and lastly graphic cards.

Pulse Width Modulation

Pulse time modulation is also know as pulse width or pulse duration modulation. It is type of analog modulation in which the time or width or say the duration of the carrier signal is proportional to the corresponding sample vale of the continuous message signal. However in this type of modulation the width changes but the amplitude remains constant.

And thus to maintain the ideal constant amplitude of the PWM signal amplitude limiters are use. This also helps in limiting the noise interference.

There are three main variation in PWM;

1. Firstly Constant starting or leading edge
2. Secondly Constant trailing or ending edge
3. And lastly central part of the pulse is constant

In all of the variation the other then the constant edge the edges changes with respect to the changes in the original message signal.

Advantages

1. Economical.
2. High power efficiency and handling capacity.
3. Easy to make.
4. Large range of frequency.
5. And lastly low rate of power consumption.

Disadvantages

1. Complexity.
2. Voltage spikes.
3. radio frequency interference and electromagnetic noise.
4. and lastly cost.

Application

1. Analog to digital converter.
2. voltage regulators.
3. And lastly power delivery.

Pulse Code Modulation

In Pulse code modulation a message signal is resented by a sequence code pulses, which is mainly accomplish by representing the signal in discrete form in both time and amplitude. In simple words it is use for conversion of continuous analog signal into equivalent discrete digital signal. Thus the output of the PCM look like a binary series.

PCM also uses sampling techniques for the conversion.

Basic Block Diagram Elements of PCM

Low Pass Filter

The Low pass filter is a type of filter that eliminates frequency bit that is higher than the highest component of the message signal i.e the cutoff frequency. Such filters are also name as high cut filters.

Sampling

The incoming analog message signal is sampled with a train of the narrow pulse so as to approximate the instantaneous sampling process. Ideally in order to ensure the complete regeneration of the message signal must be sampled at a frequency greater than twice the maximum frequency within the signal. However, practically pre-aliasing filters must be used to avoid aliasing errors.

Quantization

The version of the message signal which is a sample is then quantized, thereby providing a new representation of the signal that is discrete in both time and amplitude. In short, quantization is a process in which the numbers of samples obtained from the sampler are just put to a particular finite limit.

The quantizers can be of two type;

1. Uniform quantization (fixed step size)
   • Mid-rise
   • Mid-Tread
2. And lastly non-uniform quantization (variable step size)

Companding

Non uniform quantization can be obtain by companding

Companding refers to a technique which comprises of compression first and the expansion of analog or digital signal. It is use to reduce the large series into require number bits while the conversion of ADC while achieve a dynamic range.

Thus it is helpful in both ways, as it improves the resolution of weak signal by enlarging them or by decreasing the step size. And also helps the resolution of the strong signal by compressing them or by increasing the step size. Hence we can conclude that non uniform quantization is more effective than uniform quantization.

But the only disadvantage is that; they are complex in structure and expensive to buy.

Types of Companding

1. A law (US standard). In A law companding, uniform quantization is obtained at A=0 where the cure is linear without any compression. and also it has a mid-rise origin i.e. consists of non-zero values.
2. And lastly μ law (European standard). In μ law companding uniform quantization is obtain at μ =0 where the curve is linear and without any compression. Besides, it has a mid-tread at origin i.e consist of zero as a value.

Encoder

The encoder assigns equivalent binary values to the elected samples after the process of quantization. It is a sample and holds process.

However, the overall conversion of analog to digital signal consist of these three steps mention above. Sampler followed by quantizer and encoder.

Regenerative Repeater

It is one of the most important component of a system as during the procession of transmission in the channel a large amount of information is lost and also noise gets added to to the pulse. Thus to reobtain the lost part of the signal repeater are used after every fix interval of time.

Decoder

The purpose of the decoder circuit is to decode the signal back to its original form or the form which is require at the output. However this process is the exact opposite of encoder and thus this decoding process also goes by the name of digital to analog converter.

Regenerative filter

It is a type of low pass filter. Which is use to obtain the original signal back.

Advanatges

1. Easily available storage.
2. Transmission quality.
3. Regeneratable.
4. Lastly Noise immunity.

Disadvantages

1. Large bandwidth.
2. Does not support wireless transmission.
3. Lastly need for synchronizations.

Application

1. Telephone system.
2. Recording system (digital)

Delta Modulation

It is a type of modulation in which the rate of sampling is way higher than the Nyquist rate and also step size of the signal after quantization is also quite small and petite.

Feature of delta modulation

1. Firstly the design for quantization is simple and easy.
2. Bit rates are user-changeable.
3. The resolution is moderate.
4. Lastly easy implementation.

In other words we can say that DM is a simpler version of DPCM. DM also goes by the name 1 bit DPCM.

Block Diagram

The basic block diagram of DM consists of a simple 1-bit quantizer, a summing point, and an accumulator. Besides this, the circuit also consists of low-pass filters. The main purpose of the LPF is to remove noise.

Advantage

1. Lower bandwidth need.
2. Simple circuit design.
3. And lastly cheap.

Disadvantage

1. Granular / idle noise (when step-size is large).
2. Slope over load distortion (whenever step-size is small).

Application

1. As a type of simple DPCM.
2. DAC (Digital to analog converter).

Conclusion

Here we are at the end of the blog. I hope that you liked the content and have got all your doubts clear. as per my personal point of view pulse modulation is one of the important types of modulation as its applications are spread over a wide range. It covers from telephone systems, radio stations, ADC’s, to DAC’s so I believe that being having its knowledge increases ours core value and also helps in understanding the current mode of communications.

So if you like the blog then please do share it with others and also comment the best part. besides if you do have any doubt then please feel free to comment down and ask and will try our best to reply as early as possible.

Regards,

Have a nice day 🙂

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