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
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3. Syllabus Pulse modulation, Pulse amplitude modulation (PAM),
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DTEL
Syllabus
Pulse modulation,
Pulse amplitude modulation (PAM),
Pulse width modulation (PWM),
Pulse position modulation (PPM),
Pulse code modulation (PCM),
Delta modulation DM).
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4. DTEL
Pulse Modulation
The process of transmitting signals in the form of pulses (discontinuous signals) by using special techniques
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5. Types Pulse Modulation
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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)
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6. Pulse Amplitude Modulation (PAM)
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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.
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7. Pulse Amplitude Modulation
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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
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8. Pulse Width Modulation
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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
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9. Pulse Position Modulation
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* 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
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10. PULSE CODE MODULATION (PCM)
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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.
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11. Basic operation - PCM Sampling Quantizing Encoding
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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.
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12. The input signal Block Diagram - PCM
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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
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13. Analog to Digital Conversion
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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
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14. Quantization The output of a sampler is still continuous in amplitude.
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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
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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
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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.
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17. For One sample -- one bit transmitted
Working Principle of DM
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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
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18. Delta Modulation – Transmitter
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ERROR SIGNAL
∆sgn[e(kts}]
Last Sample
Present Sample
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19. DTEL
+ ∆ = 1 Transmitted
- ∆ = 0 Transmitted
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20. Delta Modulation – Receiver
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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.
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21. Delta Modulation – Waveform
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22. Advantages Transmit one bit/sample -
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Transmit one bit/sample -
Bandwidth & signally rate is small.
No ADC required
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23. Summary DTEL Analog Signal Pulse Amplitude Modulation
Pulse Width Modulation
Pulse Position Modulation
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24. DTEL
THANK YOU
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