运放自动调零和相关双采样技术.pdf

Circuit Techniques for Reducing the Effects of Op-Amp Imperfections: Autozeroing, Correlated Double Sampling, and Chopper Stabilization Invited Paper In linear ICs fabricated in a low-voltage CMOS technology, The purpose of the circuit techniques discussed in this the reduction of the dynamic range due to the dc offset and low- paper is to reduce the effects of the narrow-band noise ,frequency noise of the ampli$ers becomes increasingly significant. sources at the virtual ground of an op-amp stage. By Also, the achievable aniplijier gain is often quite low in such a technology, since cascoding may not be a practical circuit option reducing the low-frequency noise and offset at the op-amp due to the resulting reduction of the output signal swing. In this input, hence the dynamic range of the circuit is improved; paper, some old and some new circuit techniques will be described by reducing the signal voltage at the virtual ground ter- for the compensation of the amplifier most important nonideal minal, the effect of the finite low-frequency gain of the effects including the noise (mainly thermal and llf noise), the op-amp on the signal-processing characteristics of the stage input-referred dc offset voltage, as well as thefinite gain resulting in a nonideal virtual ground at the input. is decreased. Both improvements are especially significant for low-supply voltage circuits, which have limited signal swings and where the op-amp gain may be low