Analog/Digital Coding Bobby Geevarughese ECE-E4434/12/05

Overview Analog Signals Analog Signals Digital Signals Digital Signals A/D Coding A/D Coding D/A Coding D/A Coding

Analog Signals Sound carried as pattern of pressure waves Change in pressure is measured in each instant and voltage will vary in same way

Analog Signals

Problems Degradation Size limitations Noise Various amounts will alter reconstruction of original signal Various amounts will alter reconstruction of original signal

Digital Signals Finite values Consists of patterns of bits of information Advantage over analog signals in that precise signal level is not necessary

Digital Signals

Analog to Digital Coding Sampling Theorem Must sample at 2x the BW to perfectly reconstruct the original signal and avoid aliasing Must sample at 2x the BW to perfectly reconstruct the original signal and avoid aliasing Problem arises because values are still in continuous range and can take on any value Problem arises because values are still in continuous range and can take on any value Quantization Samples are “rounded off” to the nearest amplitude value Samples are “rounded off” to the nearest amplitude value

Analog to Digital Coding

Compact Disc Falling and rising edges of a pit correspond to the falling and rising edges of the pulse train Falling and rising edges of a pit correspond to the falling and rising edges of the pulse train Light sensor recreates sequence of 1’s and 0’s to convert back to original signal Light sensor recreates sequence of 1’s and 0’s to convert back to original signal

CD A/D Conversion Sampling rate = 44,100 samples/second 16 bits/sample (word length) needed to represent different quantization levels Quantization levels = 65,536 Sampling at this rate with this much bit resolution enables perfect reconstruction of original signal

Digital to Analog Coding Complete reversal of ADC Complete reversal of ADC

Questions?