Autozero

Autozero is a technique used in precision analog electronics to suppress or cancel the input offset voltage and low-frequency drift of amplifiers. The method relies on periodically measuring the amplifier’s own offset and subtracting it from subsequent signals, thereby improving DC accuracy without requiring expensive trimming or resistors.

Operation typically involves alternating between a reset phase and a measurement phase. During the reset phase, the input is connected to a reference (often ground) and the amplifier’s offset is measured and stored on a capacitor. In the measurement phase, the stored offset is subtracted from the amplifier’s output, effectively cancelling the offset. The cycle repeats at a rate chosen to balance drift tracking with bandwidth. Variants use two-path architectures, switches, and sample-and-hold capacitors; some designs integrate autozero with chopper stabilization to reduce 1/f noise.

Applications include precision instrumentation such as voltmeters, differential amplifiers, instrumentation amplifiers, and front ends for analog-to-digital converters. Autozero also appears in certain op-amps marketed as autozero or chopper-stabilized devices.

Advantages and limitations: Autozero can provide very low offset voltages, reduced drift, and improved DC accuracy. Drawbacks include reduced bandwidth due to switching, added circuit complexity, and potential leakage or capacitor charge injection. Modern implementations often blend autozero with other techniques, such as chopper stabilization, to minimize noise without sacrificing speed.

History and context: Autozero techniques emerged with advancements in switched-capacitor technology in the mid-20th century and became common in precision integrated circuits for instrumentation. It is distinct from general automatic zeroing used in control systems.