Analog/DigitalAnalog/DigitalCodingCoding

Bobby GeevarugheseBobby Geevarughese

ECE-E443ECE-E443

4/12/054/12/05

OverviewOverview

Analog SignalsAnalog Signals

Digital SignalsDigital Signals

A/D CodingA/D Coding

D/A CodingD/A Coding

Analog SignalsAnalog Signals

Sound carried as pattern of pressure Sound carried as pattern of pressure waveswaves

Change in pressure is measured in each Change in pressure is measured in each instant and voltage will vary in same wayinstant and voltage will vary in same way

Analog SignalsAnalog Signals

ProblemsProblems

DegradationDegradation

Size limitationsSize limitations

NoiseNoise Various amounts will alter reconstruction of Various amounts will alter reconstruction of

original signaloriginal signal

Digital SignalsDigital Signals

Finite valuesFinite values

Consists of patterns of bits of informationConsists of patterns of bits of information

Advantage over analog signals in that Advantage over analog signals in that precise signal level is not necessaryprecise signal level is not necessary

Digital SignalsDigital Signals

Analog to Digital CodingAnalog to Digital Coding

Sampling TheoremSampling Theorem Must sample at 2x the BW to perfectly reconstruct the Must sample at 2x the BW to perfectly reconstruct the

original signal and avoid aliasingoriginal signal and avoid aliasing Problem arises because values are still in continuous Problem arises because values are still in continuous

range and can take on any valuerange and can take on any value

QuantizationQuantization Samples are “rounded off” to the nearest Samples are “rounded off” to the nearest

amplitude valueamplitude value

Analog to Digital CodingAnalog to Digital Coding

Analog to Digital CodingAnalog to Digital Coding

Compact DiscCompact Disc Falling and rising edges of a pit correspond to Falling and rising edges of a pit correspond to

the falling and rising edges of the pulse trainthe falling and rising edges of the pulse train Light sensor recreates sequence of 1’s and 0’s Light sensor recreates sequence of 1’s and 0’s

to convert back to original signalto convert back to original signal

CD A/D ConversionCD A/D Conversion

Sampling rate = 44,100 samples/secondSampling rate = 44,100 samples/second

16 bits/sample (word length) needed to 16 bits/sample (word length) needed to represent different quantization levelsrepresent different quantization levels

Quantization levels = 65,536Quantization levels = 65,536

Sampling at this rate with this much bit Sampling at this rate with this much bit resolution enables perfect reconstruction of resolution enables perfect reconstruction of original signaloriginal signal

Digital to Analog CodingDigital to Analog Coding

Complete reversal of ADCComplete reversal of ADC

Questions?Questions?