Sensors, ADCs & sampling
Sensors, bridges & calibration
A sensor output is the start of a measurement, not the final answer.
Sensors convert a physical quantity into an electrical change: resistance, voltage, current, capacitance or frequency. A Wheatstone bridge compares two voltage dividers and can expose a small resistance change as a differential voltage. Signal conditioning then provides suitable gain, filtering and protection. Calibration relates the electrical result to a known physical reference and can correct offset and gain.
ADC resolution, codes & reference
More bits make smaller steps, not automatic accuracy.
An analog-to-digital converter maps an input range into discrete codes. An N-bit ADC has up to 2ᴺ codes. The reference sets the scale, so reference error becomes measurement error. Input drive, settling, noise, offset and linearity also affect performance. A digital-to-analog converter performs the reverse mapping, but its output is not automatically a perfectly smooth reconstructed signal.
Sampling, aliasing & reconstruction
A fast signal can disguise itself when you look too slowly.
Sampling records a signal at discrete times. For a band-limited baseband signal, the sample rate must exceed twice its highest frequency for ideal unambiguous reconstruction. Real designs need transition margin and an analog anti-alias filter before the ADC. Once an unwanted frequency has aliased into the band, a later digital filter cannot identify its original frequency from those samples alone.