Research And Design Of Weak Current Detection Circuit Based On Pulse Frequency Modulation

With the development of industry and the progress of modern technology,weak current detection technology has been applied to various fields and has been well developed.Nowadays,high-precision current measurement instruments can measure current up to the picoamp level,but there is still room for further improvement in terms of linearity and power consumption.In this regard,this paper designs a weak current detection circuit based on the principle of pulse-frequency modulation,which can not only improve the linearity of the conversion between current and frequency,but also reduce the power consumption of the system,making it possible to be widely used in various fields,which is of certain importance to promote the development of other fields.This thesis introduces the different methods of weak current detection circuit.By analyzing the advantages and disadvantages of various detection circuits in detail,a weak current detection circuit is designed based on double comparator on the operating principle of pulse frequency modulation,which converts the current signal to frequency signal.As a result,the current can be detected by measuring the frequency.The circuit works as follows: The main comparator(continuous time comparator)is used to constantly monitor whether the output voltage of the integrator exceeds the threshold value,and the ring oscillator is started by flipping the main comparator ahead of time,then the ring oscillator triggers the clock-controlled auxiliary comparator to start working.The auxiliary comparator is stopped by a feedback signal immediately after the result of the comparison,so the auxiliary comparator is only on for part of the cycle,which effectively reduces the power consumption of the system.In order to improve the zero-crossing detection ability of the comparator and meet the requirement of linearity in converting current into frequency,a clock-controlled high-frequency dynamic latching comparator is used for the auxiliary comparator.The switching of the ring oscillator operating state and circuit charging and discharging is achieved by a rising edge triggered D flip-flop with asynchronous reset and a basic logic gate circuit.In addition,in order to enable the main comparator to flip before the auxiliary comparator in each cycle,a band-gap reference circuit is used to generate a zero-temperature coefficient current,which is then used to obtain the reference voltages of the main and auxiliary comparators respectively by dividing the voltage through a resistor,so that the reference voltage of the main comparator is lower than the reference voltage of the auxiliary comparator.In this thesis,based on 130 nm CMOS technology,cadence virtuoso software is used to build and debug the overall circuit,and the corresponding circuit simulation and layout design is completed.When the input current is 0.4μA～4μA,the linearity of current-frequency conversion is calculated by Matlab software.The calculation results show that the linearity of current-frequency conversion is 0.82%.When the temperature range of the circuit is-40℃～85℃,the calculated temperature coefficient of the output signal frequency is 34.15ppm/℃.The power consumption is about 1.89 m W when the power supply voltage is 2V.The simulation results show that the weak current detection circuit based on pulse frequency modulation meets the design requirements of the subject.