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Analog & Mixed-Signal

ADCs, DACs, sensors, op-amps, references. Analog cares about microvolts, so the enemies are noise, grounding and placement — coupling from digital and switching circuits ruins measurements.

Grounding & placement​

  • Use a solid ground plane; don't chop it into isolated islands (modern guidance — splits cause more problems than they solve). Instead, partition by placement: keep analog parts in an analog area, digital in a digital area, over one continuous plane.
  • Keep switching regulators and fast digital away from analog front-ends and references.
  • Route digital and analog signals so they don't run parallel/overlap.

Reference & filtering​

  • Give ADC/DAC reference and supply pins their own filtering (ferrite/RC + local caps).
  • Use a clean, stable voltage reference; keep its traces short and quiet.

Sensing​

  • Use Kelvin (4-wire) sensing for shunts and precision measurements.
  • Guard high-impedance nodes; keep leakage paths clean (no flux residue).

ADC layout​

  • Place the ADC near its signal source; short analog input traces.
  • Single, clean return for the analog section; tie to the system ground at one well-chosen point near the converter.
Noise sneaks in

The most common analog bug is a switching regulator or digital bus placed next to the front-end. Fix it with placement first, filtering second.

See also​