Analog Front-end Integrated Circuit Design For Multiple Meteorological Sensor

The multi-meteorological smart sensor microsystem with the analog front-end circuit as the core is an important technical link in the current meteorological detection and disaster early warning.The analog front-end circuit is responsible for the acquisition and quantification of information,which directly determines the accuracy and speed of the acquired information.In general,the analog signal collected by the sensor is difficult to be directly processed by the microcontroller,so the analog front-end circuit is required to amplify and convert the output signal of the sensor before being processed by the subsequent system.Based on the requirements of multi-meteorological smart sensor microsystem,an analog front-end circuit for multi-meteorological sensors which includes LDO,programmable gain amplifier,SAR ADC,and humidity measurement circuit is designed.First of all,the overall structure of the analog front-end circuit is determined based on the analysis of the principle and performance of different functional meteorological sensors.Secondly,in order to better design the circuit,the basic working principle and performance parameters of the key circuits of the analog front-end are introduced respectively.Then,for the LDO without off-chip capacitor,a source follower with negative feedback loop is designed and based on it,a nested Miller compensation method is adopted to further improve the loop stability.For the programmable gain amplifier,a fully differential programmable gain amplifier consisting composed of a rail-to-rail input stage with an instrumentation amplifier structure,a rail-to-rail auto-zero fully differential operational amplifier,a digital control circuit,and a DC offset compensation circuit is designed to suppress common mode noise of sensor,DC offset and LDO output noise,while continuous time Auto-Zero calibration technology is applied to reduce its input offset voltage.For the 14-bit SAR ADC,a differential structure is used to improve its own conversion accuracy and common mode noise suppression capability,at the same time,a gate voltage bootstrap switch with clock feedthrough compensation technology is designed to further improve the conversion accuracy.In order to reduce the average power consumption and area of CDAC,a segmented differential DAC capacitor array based on the V_CM-based switching strategy is designed.Finally,based on the principle of the relationship between the capacitance value of the humidity sensor and the frequency of the rectangular wave,a humidity measurement circuit is designed.Based on Hua Hong’s 0.18μm process and Cadence platform,the circuit design,pre-simulation,layout design and post-simulation of the multi-meteorological sensor analog front-end circuit are completed.The post-simulation results show that the LDO without off-chip capacitor has a phase margin greater than 74°under different temperature combinations of 5 process angles,and has good loop stability.Under 100 Monte Carlo simulations of the programmable gain amplifier,the-1σvalues of the power supply rejection ratio and common mode rejection ratio at 1 k Hz are 100.4 d B and 107.5 d B respectively,and the 1σvalue of the input offset voltage is 22μV.The frequency error of the humidity measurement circuit is 0.03%,and the accuracy reaches 99.97%.The LDO,programmable gain amplifier and 14-bit SAR ADC are connected as a whole,and a low-frequency sine wave signal with a frequency of 244.1406 Hz and a small amplitude is given at the input end,the circuit as a whole can realize the function of amplifying the input analog signal and finally outputting the digital code,its effective number of bit（ENOB）is 11.40 bit,SINAD is 70.37d B,SNR is 71.05 d B,SFDR is 83.85 d Bc,and THD is-78.55 d B.The results have certain reference value for the related design of analog front-end circuits for multi-meteorological sensors.