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Delta Modulation

Delta Modulation. Professor: Dr. Miguel Alonso Jr. Outline. Delta Modulation Continuously variable slope delta modulation Demodulation. Delta Modulation. Next form of pulse modulation

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Delta Modulation

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  1. Delta Modulation Professor: Dr. Miguel Alonso Jr.

  2. Outline • Delta Modulation • Continuously variable slope delta modulation • Demodulation

  3. Delta Modulation • Next form of pulse modulation • Transmits information only to indicate whether the analog signal that is being encoded goes up or goes down • The Encoder Outputs are highs or lows that “instruct” whether to go up or down, respectively • DM takes advantage of the fact that voice signals do not change abruptly

  4. The analog signal is quantized by a one-bit ADC (a comparator implemented as a comparator) • The comparator output is converted back to an analog signal with a 1-bit DAC, and subtracted from the input after passing through an integrator • The shape of the analog signal is transmitted as follows: a "1" indicates that a positive excursion has occurred since the last sample, and a "0" indicates that a negative excursion has occurred since the last sample.

  5. DM Block Diagram

  6. Resulting Waveforms

  7. Simple Implementation of a DM system

  8. Limitations of the system • Slope overload • When the analog signal has a high rate of change, the DM can “fall behind” and a distorted output occurs

  9. Tradeoffs • Simplicity versus Quality • In order to obtain the high quality DM requires very high sampling rates, typically 20× the highest frequency of interest, as opposed to Nyquist rate of 2×

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