chopperstabilized

Chopper-stabilized is a term used for electronic circuits and sensors that employ a chopping (modulation) technique to suppress offset voltages and low-frequency (1/f) noise. By periodically modulating the input with a square-wave switch, these devices achieve remarkable dc accuracy and stability, often in instrumentation amplifiers and electrometer-grade front ends.

Operation involves a periodic switch that multiplies the input by a square wave, shifting the signal spectrum to a carrier frequency. The amplifier then amplifies the modulated signal, and a demodulator (often the same switch in inverse phase) recovers the original signal at baseband. The process also acts as a high-pass reference for offset and drift, so slow variations are suppressed. Practical implementations require careful clocking to minimize switching artifacts such as clock feedthrough and charge injection, and often use correlated double sampling or auto-zero techniques to further reduce residual errors.

Advantages and trade-offs: The primary benefit is ultra-low input offset and low 1/f noise, enabling accurate dc measurements and high-stability amplification. Trade-offs include a residual ripple at the chopping frequency, increased circuit complexity, higher power consumption, reduced bandwidth (the chopping frequency sets a practical limit), and potential degradation of large-signal performance.

Applications: Chopper-stabilized circuits are used in precision instrumentation amplifiers, ADC front-ends, electrometers, thermocouple amplifiers, and DC voltmeters. The technique is related to but distinct from auto-zero amplifiers; both aim to reduce offset but use different approaches. History: the method was developed in the mid-20th century and has been widely implemented in monolithic integrated circuits since the 1960s.