Study And Design Of Operational Amplifier Based On Metal Oxide TFT

Metal oxide thin film transistor(MO TFT)shows enormous potential in transparent and flexible electronics,such as lost-cost RFIID/NFC tags and bio-potential monitoring system,due to the advantages of high mobility,low cost,simple preparation process,the ease in fabrication of large-area and compatibility with flexible substrates.Among them,the operational amplifier(OPAMP)is the most important module in analog circuits.For the development of transparent and flexible electronics,it is important for metal oxide TFTs realizing operational amplifiers used to amplify,collect and transmission signalsThis paper describes the process technology and the electrical characteristics of MO TFT,including the transfer characteristics,output characteristics,C-V characteristics,intrinsic gain secondary effects and small signal model,And the experimental extraction values of the main parameters are listed.Based on the characteristic measurement,the simulation model of MO TFT is fitted,and the main parameters of the model fitting are listed.After introducing three typical gain-enhancement techniques:gain-boost,capacitive-boost and transconductance-enhancement,the working principle and performance characteristics of a gain-enhancement operational amplifier based on double positive feedback are analyzedTo solve the problems of low mobility and non-complementary P-type devices in MO TFT devices,this paper proposes a cross-coupled operational amplifier based on positive feedback technology.According to the different connection methods,the cross-coupled operational amplifier can be divided into three type:common drain amplifier,common gate amplifier and common source amplifier.Then,we analyzed the design principle and performance of these three cross-coupled operational amplifiers,which performance verification through simulation and tape-out test.The results show that under the same power supply voltage,compared with the other two type cross-coupled amplifiers,the common drain amplifier has the lowest static power consumption,the common gate amplifier has the widest bandwidth,and the common source amplifier has a higher open-loop differential gain and output voltage swing,and its bandwidth is relatively high.The common-source cross-coupled operational amplifier has an open-loop differential gain(Av)of 23.83 dB over a 3 dB bandwidth of 0.4 kHz at a supply voltage of 15 V.The unity-gain frequency,phase margin,output and input voltage swing are 3.55 kHz,94.03°,1.44 V and 60 mV,respectively.Therefore,the common source cross-coupled operational amplifier is more suitable for designing the high-performance operational amplifier based on MO TFT.To further provide the open-loop gain of MO TFT amplifier,a multistage amplifier cascaded by a common-source cross-coupled operational amplifier,a differential-to-single-ended converter and a single-ended common source amplifier is proposed.This OPAMP has an open-loop differential gain(Av)of 27.70 dB over a 3dB bandwidth(BW)of 1.528 kHz at a supply voltage of 15 V.The unity-gain frequency,phase margin and DC power consumption(PDC)are 37.3 kHz,31.48°PM and 0.137 mW,respectively.The results show that this multi-stage OPAMP can effectively improve the voltage gain and output swing.In order to improve the linearity and stability of the MO TFT OPAMP,an improved multistage operational amplifier is proposed based on the above multistage amplifier structure.The simulation results show that the linearity of cross-coupled OPAMP can be improved by connecting a transistor operating in the linear region at the drain of the differential input tube.And the miller compensation method can increase the phase margin of two-stage OPAMP and improve its stability.