CurrentSwitched R2R DAC

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Current-Switched R-2R DAC
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Voltage-Switched R-2R DAC
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DAC Non-Linearities
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DAC Gain Offset Errors
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Direct (Flash) ADC
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Successive Approximation ADC
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Integrating ADCs
  

•          There is a whole family of these
  circuits
• o        single-slope
• o        dual-slope
• o        multi-slope
• o        charge balance, PWM
• o        sigma-delta (?-?) (order 1 to m)
• None need a T(S)/H, (but may be useful)
•   All integrate the input signal for a fixed
  time and then digitize it
• conversion time up to 2 x 2n 2n1 clock
  periods
•   However, the last 2 types integrate
  continuously
•   All allow increased resolution but are slower
  than the ?-? type

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Dual-Slope ADC
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Integrator Output Waveforms
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Multi-Slope ADC

• To increase resolution, the comparator threshold
  becomes the limiting factor
• Multi-slope uses smaller and smaller reference
  values to progressively approach the comparator
  zero at a slower rate
• Each reference period de-integrates the
  remaining error
• Very much more complex circuit and costly
• Much faster than Dual-Slope for the same
  resolution - used in some DVMs
• May also be used with Charge-Balance

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Charge-Balance ADC
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Integrator Output Waveforms
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Charge Balance Performance

• Integrates signal and reference signals
  continuously
• I0 VREF/R then VIN VREF.Count/CountMax
• Reduces integrator capacitor error of Dual-Slope
• Capable of 10-8 (26-bit) performance, if you can
  wait - speed v resolution
• DVM type ADC PWM variants

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Sigma-Delta ADC (1)

• Recent variant of Delta modulator and
  Charge-Balance concepts
• Originally used for audio only, now used from
  dc to rf
• Very high resolution up to 22bits and very
  fast 1000x faster than dual-slope
• Very complex internal operation but quite
  simple analog circuitry
• Uses a special (decimating) digital filter
• Can be integrated with µCs etc
• Minimal chip cost but support circuits
  still expensive for ultra-high performance

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Sigma-Delta ADC (2)