Design Of Weak Current Sensing Amplifier Based On Correlated Double Sampling

With the continuous development of science and technology,weak electrical signal detection technology is widely used in various fields.The size of semiconductors continues to shrink,and the accuracy of weak current detection is getting higher and higher.Designing and implementing a high-precision weak current detection circuit is a key research topic in many fields.Therefore,the study of weak current detection amplifier circuits is of great significance.In order to achieve p A level resolution,this paper selects the capacitor as the charge integrator of the feedback element to avoid the current noise of the resistance element.In order to further eliminate the interference of the low-frequency noise of the amplifier on the current detection,this paper further applies the Correlated Double Sampling technology in the charge integrator and adds an offset storage capacitor at the output of the amplifier.With the help of switches and clock,the circuit can be reset to zero and the signal can be amplified alternately.The weak current front-end amplifier circuit proposed in this paper has complex transconductance,switch and capacitor connections,and the timing of switch switching also retains the correlation between noise.In order to accurately calculate the output noise and current resolution of the amplifier circuit,this paper analyzes in detail the generation and transfer of noise in the switching process,and gives the analytical expression of the output noise.According to the deduced analytical expression of output noise,the Matlab program is written to realize the rapid evaluation of the performance of the amplifier circuit and the optimization of the circuit parameters.The current signal to be tested is a single-ended input,and the single-ended signal has poor anti-interference ability.It is converted into a differential output through a circuit.There is an error in the conversion of single-ended to differential mode.In addition,unnecessary errors in charge injection and clock feedthrough will be introduced during the MOS switch off process,so consider adding a Dummy structure with no current input.In order to meet the requirements of low noise and wide common mode range for signal detection,the op amp in the charge integrator uses a differential input folded common-source cascode amplification structure.Gain-boosting structure is added to obtain higher gain to suppress the noise of the subsequent detection circuit.Correlated double sampling adopts the closed-loop output offset storage scheme.According to the calculated noise analysis expression,the MOS switch with ultra-low drain current is designed to reduce the sampling frequency and obtain better current resolution.The clock circuit converts the off-chip input square wave signal with unknown duty cycle into a non-overlapping clock,providing the circuit with a reset,auto-zero,and amplification stage clock.Build and debug the circuit based on the 0.18?m process,complete the layout design and post-simulation.The frequency response of the simulated op amp is 113 dB,and the noise is 46.92 nV/(?).The pnoise simulation results are equivalent to input current noise of about 0.86 pA/(?)@1Hz and 0.086 pA/(?)@10Hz.The preamplifier circuit for weak electrical signal detection based on the correlated double sampling circuit designed in this paper meets the design requirements of the subject,and can detect weak current well on the basis of noise suppression.