Design And Test Of Weak Current Conditioning Amplifier Chip

With the rapid development of semiconductor technology,weak electric current detection techniques have been widely used in many fields,the resolution of weak current detection technology is becoming more and more demanding.High resolution means that weaker current can be detected,and the weak currents generated in many fields have reached the sub-pA level,which brings great challenges to the weak current detection technology.In order to meet the challenge of weak current detection technology,it is of great significance to design a weak current conditioning amplifier chip with high resolution.In order to achieve the current resolution of sub-pA level,this thesis constructs a weak current detection scheme based on the traditional charge integrator,and proposes a low-noise current amplifier circuit.The weak current detection adopts the charge integrator as the front-end solution to reduce the influence of thermal noise.In order to suppress and eliminate the kT/C noise in the charge integrator circuit,the correlated double sampling technique is used.In order to understand the effect of noise on the current resolution,analyzing the noise transfer process and circuit non-ideal characteristics in the amplifier circuit,the Allan variance is introduced to evaluate the current resolution.The signal to be measured adopts the single-ended current input method.In order to solve the problems of charge injection and clock feed-through existing in the single-ended switching capacitor circuit,a pseudo-differential amplifier structure is designed and an additional input common-mode feedback circuit is added.Weak current signal requires higher gain of the amplifier.In order to achieve gain above 100dB,we use the gain bootstrap technique to increase the gain.In order to reduce the noise contribution of the output stage tail current tube,source degeneration resistors are added to the source ends of the four tail current tubes using source degeneration technology.Analyzing the characteristics of weak current signal,design test scheme and hardware circuit,complete schematic diagram and PCB drawing,and use shielding measures to reduce external electromagnetic interference.The front end of the test circuit uses photodiode to generate weak current signal.The weak current signal is sent to the chip under test to generate differential voltage signal,and then the voltage signal is conditioned and amplified by the amplifier circuit to achieve inphase amplification and differential conversion to single-ended,and finally output to the signal analyzer.The principle and procedure of the test are described in detail,the test is carried out from the two aspects of signal-to-noise ratio and Allan variance,and the test results are analyzed to calculate current resolution.SMIC 0.18μm CMOS process is used to complete the design of the entire weak current conditioning amplifier chip,and the circuit design and simulation are completed in the Cadence software.After post-simulation analysis,the gain of the main operational amplifier reaches 115.1dB,the equivalent input noise is 17.78nV/(?),and the entire chip area is 956μm×1056μm.The current resolution of the chip is tested based on SNR and Allan variance.The test results show that the minimum current resolution based on SNR is 0.036pA,and the minimum current resolution based on Allan variance is 0.035pA,both of which reach the sub-pA level.