适用于微弱信号检测的低噪声仪表放大器

Low Noise Instrumentation Amplifier for Small Signal Detection

为解决传统仪表放大器的噪声与纹波等问题,设计了一种能测量微弱电信号的低噪声电容耦合斩波仪表放大器(CCIA:Capacitively-Coupled Chopper Instrumentation Amplifier),实现了极低的增益误差与等效噪声。通过采用斩波结构使输入共模电压达到轨对轨范围;两级折叠式共源共栅放大器能有效地提升开环增益;同时,纹波减少环路(RRL:Ripple Reduction Loop)可抑制CCIA输出端的斩波纹波;可调正反馈回路(TPFL:Tunable Positive Feedback Loop)能提升CCIA的输入阻抗;最后,直流伺服回路(DCL:DC Cancellation Loop)能抑制电极偏移并有利于微弱信号检测。CCIA采用标准0. 18μm CMOS工艺实现,仿真结果表明,电路的增益误差为0. 11%,在100 Hz下,等效输入参考噪声为6. 98 n V。

A low noise capacitively-coupled chopper instrumentation amplifier which is able to measure small signals is proposed.In this design,chopper is adopted which can make the input common-mode voltage achieve a rail-to-rail range and also has a low power consumption.A two stage folded-cascode opamp is employed to boost the open-loop gain effectively.Furthermore,a ripple reduction loop is used to suppress the chopping ripple at the output of the CCIA(Capacitively-Coupled Chopper Instrumentation Amplifier).A tunable positive feedback loop based on the MOS capacitors is adopted to boost the input impedance of the CCIA opamp.At last,a DC(Direct Current)cancellation loop is introduced to suppress the electrode offset and to facilitate the weak signal sensing.The CCIA is implemented in a standard 0.18μm CMOS(Complementary Metal Oxide Semiconductor)process.Simulation results show that the gain inaccuracy of proposed CCIA is 0.11%and the input referred noise is 6.98 nV at 100 Hz.