Analog, Digital, and Conversion

Sources Of PCM "Approximation"

  • Band-limited via Nyquist (approximation in time)

  • Quantization due to finite representation (approximation in amplitude)

  • Assumes an idealized sampling clock — clock "skew" and "jitter" is a thing for real clocks

Digital To Analog Conversion

  • Need to take a binary number to a voltage

  • Classic method: direct conversion via R/2R Ladder

    • Very fast, simple

    • Accuracy issues are real: bit voltages and component values must be matched pretty exactly

  • Classic method: Pulse Width Modulation (PWM)

    • Digital all the way to single-wire output

    • Arbitrary resolution dependent on timing

    • Really hard to get the filtering right for audio applications: want super-high pulse rate

  • Fancy methods: can talk about later if folks are interested

Analog To Digital Conversion

  • Convert voltage on wire to binary number

  • This is the "hard" direction: the DAC tricks aren't invertible

  • One common approach uses some combination of DACs and comparators to try to make the DAC output match the analog input

  • Discussion

Last modified: Tuesday, 31 March 2020, 8:00 PM