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Analog/Digital Coding

Analog/Digital Coding. Bobby Geevarughese ECE-E443 4/12/05. Overview. Analog Signals Digital Signals A/D 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.

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Analog/Digital Coding

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  1. Analog/DigitalCoding Bobby Geevarughese ECE-E443 4/12/05

  2. Overview • Analog Signals • Digital Signals • A/D Coding • D/A Coding

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

  4. Analog Signals

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

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

  7. Digital Signals

  8. Analog to Digital Coding • Sampling Theorem • 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 • Quantization • Samples are “rounded off” to the nearest amplitude value

  9. Analog to Digital Coding

  10. Analog to Digital Coding • Compact Disc • 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

  11. 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

  12. Digital to Analog Coding • Complete reversal of ADC

  13. Questions?

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