A Programmable Gain Amplifier Design For Pressure Sensors

The analog front-end circuit(AFE)represented by the sensor's readout circuit is an important technical about IoT.It undertakes the task of acquiring and quantifying information,and directly determines the accuracy and speed of information acquisition.The programmable gain amplifier is one of the core blocks in the AFE.Its important function is to accurately amplify the output signal of the sensor and eliminate the offset voltage of the sensor output.This paper is designed as a PGA block for pressure sensor readout circuits.First of all,the PGA has an amplification function,which can amplify the weak output signal of the sensor,and it can effectively improve the accuracy of the analog-to-digital converter(ADC)and greatly improve the design accuracy of the entire AFE.Secondly,the PGA has the function of adjusting the amplification factor,which can adapt to different sensor outputs and the quantization accuracy requirements of the ADC,so it increases the scalability of the PGA.Finally,the PGA can effectively calibrate the offset voltage of the sensor output,while the PGA can also correct its own offset voltage.Together,they form a complete set of calibration algorithms that are compatible with normal working timings,which facilitates the design of logic control and greatly improves the accuracy of PGA output.First of all,this paper introduces the basic principles and main design methods of PGA,and briefly introduces the design principles of various PGAs.After that,this paper focuses on the PGA structure designed in this paper,analyzes the transfer function of each PGA three-stage op amp,and designs the open-loop op amp,the RDAC used for calibration and the bias source circuit for the reference voltage of the whole circuit.And the calculation of the relevant parameters provides a way to design a specific circuit implementation.Then the paper analyzes the source of error in the PGA circuit,proposes the auto-zero calibration structure of the auxiliary op amp,and calculates the input offset voltage from the sensor.A two-stage RDAC calibration algorithm is proposed to solve the input offset voltage.Finally,the design of this paper is drawn into the layout,and the layout of the key modules is completed,and the performance of the critical circuit modules is verified by post-layout simulation.The overall layout is completed and the simulations verify the accuracy of the two-stage RDAC calibration algorithm.This paper designs a PGA for pressure sensor.Based on the 0.18 um CMOS process,it is required to realize 4-bit pressure recognition at the sensor output.The refresh frequency of each column sensor is 100 Hz,and the performance is required to be stable.The entire PGA consists of a three-stage operational amplifier and a two-stage calibration RDAC,as well as a bias source circuit that provides a reference voltage to the module.The total layout area is 998?m×443?m.The power supply voltage range is 2.6V-3.6V,and the typical value is 2.8V.Through post-simulation,it is possible to achieve precise amplification with a magnification of-4dB-63.7dB within the specified refresh time.And when the power supply voltage is 2.6V and the input offset is 520 mV,the offset can be calibrated to 13.46?V remaining.The total PGA supply current is up to 616?A.