Research And Design Of High Performance Voltage Buffer

As one of the extremely important application circuits of operational amplifier,voltage buffer is widely used in analog or analog-digital hybrid very large scale integration design because of their high input impedance and low output impedance,which can realize various functions of impedance matching,voltage following and low resistance load driving.With the continuous reduction in the size of complementary metal-oxide-semiconductor(CMOS)devices,the development of portable wireless devices and high-speed communication systems has been greatly promoted,which causes higher requirements are put forward for the research and design of voltage buffer in terms of performance such as power consumption,voltage swing,output impedance and speed.In the paper,the research background,significance and development status of voltage buffers at home and abroad are clarified firstly and its development trends are summarized.Next,the basic principle of voltage buffer is introduced comprehensively,which include its main functions,structural characteristics and standard implementation form,and based on its standard implementation form,the function characteristics and basic implementation form of input stage,output stage and negative feedback network are described detailedly.Then,the key performance indexes of voltage buffer are given and briefly explained.Next,the high performance of voltage buffer in low output impedance and wide voltage swing are mainly studies in the paper.In order to achieve extremely low output impedance and significantly improve the loading capacity of the voltage buffer,the output impedance of flipped voltage follower(FVF)circuit is strictly deduced,based on which the transconductance-boosted technique is proposed to further attenuate the impedance of FVF,then a voltage buffer based on transconductance-boosted FVF is designed.And to ensure the stability of the voltage buffer,the dominant-pole compensation technique is used for frequency compensation.In order to greatly expand the input and output voltage swing of the voltage buffer,a rail-to-rail voltage buffer is designed.Among it,a more flexible and accurate constant-transconductance control method based on current mirror technique is proposed to solve the problem of excessively large transconductance change rate of rail-to-rail input stage,and the floating current source is used to achieve the high-efficiency bias of rail-to-rail class AB output stage.A frequency compensation circuit is also designed based on the Cascode Miller compensation principle,which aims to ensure the stable operation of the voltage buffer.Finally,the two voltage buffers are both implemented based on 0.18?m CMOS technology.The circuit schematic diagrams are drawn with Cadence software,and then the circuits are simulated by Specture software.Simulation results show that the two voltage buffers designed in the paper satisfy all the design requirements and have good performance.Among them,the open-loop output impedance of the voltage buffer based on the transconductance-boosted FVF is as low as 0.26?,which achieves an ultra low output impedance and owes a very strong load driving capacity.The input and output voltage range of the rail-to-rail voltage buffer are both 0?3.3V,which achieves the input and output voltage swing from rail to rail.At the same time,the maximum transconductance change rate of the input stage is only 2.8%,which means the transconductance of input stage is almost constant.