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