精密运算放大器

A precision op amp is an operational amplifier engineered to minimize DC errors in signal conditioning circuits. It is distinguished by very low input offset voltage and offset drift, plus low bias-current error, low-frequency noise, and strong CMRR and PSRR. Select one by comparing maximum specifications, long-term stability, supply range, source resistance, load, and temperature against the application’s accuracy requirements.

General-purpose op amps are useful when offset, drift, bias-current error, low-frequency noise, or gain error from a general-purpose device would exceed the system budget. Compare maximum specifications and total error across temperature, supply, common-mode voltage, source resistance, load, and time. A suitable precision amplifier can minimize the calibration burden, but it does not necessarily eliminate calibration.

A chopper amplifier, within the broader zero-drift category, uses chopping, auto-zeroing, or both to reduce offset and low-frequency voltage noise. Performance is device-specific. Check offset, drift, ripple, switching artifacts, voltage and current noise, aliasing, bandwidth, overload recovery, and settling rather than assuming every chopper achieves a particular offset or near-zero temperature drift.

Place the precision op amp as a low-impedance buffer between the signal source and the ADC input. Co-design the series resistor and shunt capacitor with the ADC input network to reduce kickback and noise without causing incomplete settling or instability. Verify acquisition-time settling, drive current, common-mode range, output headroom, integrated noise, distortion, capacitive-load stability, and multiplexer step size.

Temperature variation causes input offset voltage drift (TCVos), directly degrading DC accuracy. A general-purpose op amp drifting at 5 μV/°C introduces 500 μV of error across a 100°C range. Add offset at the reference temperature, and include bias-current behavior, gain, CMRR, PSRR, source resistance, resistor drift, long-term drift, supply variation, and the actual temperature excursion in the complete error budget.