Introduction

This section examines the critical parameters of amplifiers for use in precision signal conditioning applications. Offset voltages for precision IC op amps can be as low as 10 ?V with corresponding temperature drifts of 0.1 ?V/ C. Chopper stabilized op amps provide offsets and offset voltage drifts which cannot be distinguished from noise. Open loop gains greater than 1 million are common, along with common mode and power supply rejection ratios of the same magnitude. Applying these precision amplifiers while maintaining the amplifier performance can present significant challenges to a design engineer, i.e., external passive component selection and PC board layout.

It is important to understand that DC open-loop gain, offset voltage, power supply rejection (PSR), and common mode rejection (CMR) should not be the only considerations in selecting precision amplifiers. The AC performance of the amplifier is also important, even at low frequencies. Open-loop gain, PSR, and CMR all have relatively low corner frequencies, and therefore what may be considered low frequency may actually fall above these corner frequencies, increasing errors above the value predicted solely by the DC parameters. For example, an amplifier having a DC open-loop gain of 10 million and a unity-gain crossover frequency of 1 MHz has a corresponding corner frequency of 0.1 Hz! One must therefore consider the open loop gain at the actual signal frequency. The relationship between the single-pole unity-gain crossover frequency, f _u, the signal frequency, f _sig, and the open-loop...