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Meghe Group of Institutions

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Presentation on theme: "Meghe Group of Institutions"— Presentation transcript:

1 Meghe Group of Institutions
Department for Technology Enhanced Learning

2 DTEL Department of Electronics & Telecommunication VI SEM Pulse Modulation UNIT- IV Introduction to Pulse Modulation UNIT- IV

3 Syllabus Pulse modulation, Pulse amplitude modulation (PAM),
DTEL DTEL Syllabus Pulse modulation, Pulse amplitude modulation (PAM), Pulse width modulation (PWM), Pulse position modulation (PPM), Pulse code modulation (PCM), Delta modulation DM). UNIT- IV

4 DTEL Pulse Modulation The process of transmitting signals in the form of pulses (discontinuous signals) by using special techniques UNIT- IV

5 Types Pulse Modulation
DTEL Types Pulse Modulation Pulse Modulation Analog Pulse Modulation Digital Pulse Modulation Pulse Amplitude (PAM) Pulse Code (PCM) Delta (DM) Pulse Width (PWM) Pulse Position (PPM) UNIT- IV

6 Pulse Amplitude Modulation (PAM)
DTEL Pulse Amplitude Modulation (PAM) Pulse Amplitude Modulation (PAM): * The signal is sampled at regular intervals such that each sample is proportional to the amplitude of the signal at that sampling instant. This technique is called “sampling”. * For minimum distortion, the sampling rate should be more than twice the signal frequency. UNIT- IV

7 Pulse Amplitude Modulation
DTEL Pulse Amplitude Modulation PAM Analog Signal AND Gate FM Modulator Pulse Shaping Network PAM - FM Pulses at sampling frequency HF Carrier Oscillator Analog Signal Train of pulses Pulse Amplitude Modulation UNIT- IV

8 Pulse Width Modulation
DTEL Pulse Width Modulation * In this type, the amplitude is maintained constant but the duration or length or width of each pulse is varied in accordance with instantaneous value of the analog signal. * The negative side of the signal is brought to the positive side by adding a fixed d.c. voltage. Analog Signal Train of pulses Pulse Width Modulation UNIT- IV

9 Pulse Position Modulation
DTEL * In this type, the sampled waveform has fixed amplitude and width whereas the position of each pulse is varied as per instantaneous value of the analog signal. * PPM signal is further modification of a PWM signal. It has positive thin pulses (zero time or width) corresponding to the starting edge of a PWM pulse and negative thin pulses corresponding to the ending edge of a pulse. PWM PPM UNIT- IV

10 PULSE CODE MODULATION (PCM)
DTEL PULSE CODE MODULATION (PCM) DEFINITION: Pulse code modulation (PCM) – is a signal coding method of modulation in which the message signal is sampled & the amplitude of each sample is rounded off to the nearest one of a finite set of discrete level. UNIT- IV

11 Basic operation - PCM Sampling Quantizing Encoding
DTEL Basic operation - PCM The PCM signal is generated by carrying out three basic operations: Sampling Quantizing Encoding Sampling operation generates a flat-top PAM signal. Quantizing operation approximates the analog values by using a finite number of levels. This operation is considered in 3 steps Uniform Quantizer Quantization Error Quantized PAM signal output PCM signal is obtained from the quantized PAM signal by encoding each quantized sample value into a digital word. UNIT- IV

12 The input signal Block Diagram - PCM
DTEL The input signal Block Diagram - PCM is sampled prior to digitisation and an approximation to the input is reconstructed by the digital-to-analogue converter: input Sampler Quantizer Encoder Transmission Wire/optical fibre Aerial/free-space Filtering Digital-to-analogue conversion Decoder output UNIT- IV

13 Analog to Digital Conversion
DTEL The Analog-to-digital Converter (ADC) performs three functions: Sampling Makes the signal discrete in time. Quantization Makes the signal discrete in amplitude. Round off to one of q discrete levels. Encode Maps the quantized values to digital. Analog Input Signal Sample ADC Quantize 111 110 101 100 011 010 001 000 Encode Digital Output Signal UNIT- IV

14 Quantization The output of a sampler is still continuous in amplitude.
DTEL The output of a sampler is still continuous in amplitude. Each sample can take on any value e.g , 0.001, etc. The number of possible values is infinite. To transmit as a digital signal we must restrict the number of possible values. Quantization is the process of “rounding off” a sample according to some rule. E.g. suppose we must round to the nearest tenth, then: > > 0 UNIT- IV

15 DTEL PCM… ADCs are used to convert an analogue input voltage into a number that can be interpreted as a physical parameter by a computer. 0000 1111 1110 1101 1100 1011 1010 1001 0001 0010 0011 0100 0101 0110 0111 0000 0110 0111 0011 1100 1001 1011 UNIT- IV

16 DTEL Delta Modulation (DM) Need of Delta Modulation : - In PCM, transmit all bits of code words, hence need more BW & signalling rate To overcome this prob. Delta Modulation Output of DM is a single bit. UNIT- IV

17 For One sample -- one bit transmitted
Working Principle of DM DTEL Present Sample Value compared with Previous Sample Diff. - ∆ ∆ -- (+) ve -- Signal Increased by One step i.e ∆ Transmitted ∆ -- (-) ve -- Signal Decreased by One step i.e ∆ Transmitted --- 0 For One sample -- one bit transmitted UNIT- IV

18 Delta Modulation – Transmitter
DTEL ERROR SIGNAL ∆sgn[e(kts}] Last Sample Present Sample UNIT- IV

19 DTEL + ∆ = 1 Transmitted - ∆ = 0 Transmitted UNIT- IV

20 Delta Modulation – Receiver
DTEL Accumulator Accumulator generates staircase approx signal Delayed by one sampling period Ts Added to i/p signal If i/p 1 – it adds +∆ to previous / delayed signal. 0 – it substracts. LPF – Smoothens staircase signal. UNIT- IV

21 Delta Modulation – Waveform
DTEL UNIT- IV

22 Advantages Transmit one bit/sample -
DTEL Transmit one bit/sample - Bandwidth & signally rate is small. No ADC required UNIT- IV

23 Summary DTEL Analog Signal Pulse Amplitude Modulation
Pulse Width Modulation Pulse Position Modulation UNIT- IV

24 DTEL THANK YOU UNIT- IV


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