Research And Design Of High Precision R-2R Digital To Analog Converter

With the advent of the information age,more and more electronic products and industrial equipment tend to be digital,and analog equipment is replaced by digital equipment with stronger anti-interference ability and higher reliability.Digital to analog converter(DAC)is a device that converts digital signals into analog signals.With the rapid development of digital,the research direction of DACs tends to be high precision,high speed and low cost.In this paper,a high precision R-2R digital to analog converter used in MEMS gyroscope is designed.MEMS,or micro-electro-mechanical system,is a device that converts small physical changes into detectable voltages.In the MEMS gyroscope,the digital to analog converter is used to provide a sinusoidal signal in a small frequency range,keeping the silicon chip in a resonant state.When the gyro vibrates or is disturbed,the change in the gyro vibration axis will be coupled to the detection axis,and the change in angular rate will be converted into the change in displacement.By detecting the voltage at both ends of the variable capacitance,the angular rate of the gyro can be obtained.This is the working principle of the MEMS gyroscope.In this context,the frequency range of sine wave signal provided by DAC is very small,which is close to the fixed frequency.This paper first introduces the working principle of DACs,summarizes the classification of DACs,divides DACs into unitary DAC,binary DAC and segmented DAC which has many kinds of structures according to the weight of each DAC,and analyzes the advantages and disadvantages of each structure.Segmented DAC has good monotony and occupies less area,so the high-precision R-2R DAC adopts a segmented structure combining thermometer structure and R-2R structure.In this paper,the optimal proportion of segmented DAC is discussed,and the segmented structure of "14+6" is determined.The switch architecture of R-2R DAC is discussed,including the traditional switch architecture,the switch architecture that contains the bridge resistance,and the switch architecture that offsets the switch resistance.The paper also presents a method to improve the temperature characteristics of digital to analog converter.The chip designed in this paper mainly consists of three parts: reference voltage source,weighted network and drive circuit.The reference voltage is provided by the low dropout regulator(LDO).The weighted network includes resistance network,analog switch and decoder circuit.The analog switch uses CMOS switch with lower conduction resistance and faster transmission speed.The drive circuit consists of a two-stage operational amplifier,which guarantees the drive capability of DAC.After completing the circuit design and simulation of each module of the chip,the layout design of DAC was carried out according to the principle of analog layout design proposed in this paper,and it passed DRC verification and LVS verification.After the layout design is completed,the layout parasitic parameter extraction and post simulation are carried out,and the simulation results are consistent with the previous simulation results,indicating that the backend design is completed,the layout does not need to be modified and improved later,and can be directly sent to the OEM for production.The simulation results show that the output dc voltage fluctuates less than 1.15?V in 10 s working time.The DAC can work normally within the temperature range of-50? to 100?,and the temperature drift of the output signal is less than 10.2 ppm/?.The spectrum of the output single frequency sinusoidal signal shows that the SNDR of signal is 86 dB,and the actual accuracy of the digital to analog converter can reach 14 bits,which can fully satisfy the narrowband application in MEMS system.