A Design Study Of A High Speed DA Converter

With the application of DAC(Digital to analog converter)in display and communication,high-speed and high-precision DAC is becoming the goal of design.In view of display aspect,this paper designs a 8 bit high speed and high accuracy current steering DAC.This paper first investigates the status and background of the development of DAC at home and abroad,and points out the significance of high speed and high precision DAC.Then,the basic principles,performance parameters and main types of DAC are introduced,and the necessary formulas are summarized.Current DAC is selected as our research goal.After that,the main error sources of DAC are analyzed,and the three decoding methods of DAC are analyzed.The advantages and disadvantages of thermometer code,binary code and segmented decoding are analyzed.Finally,the four bit binary code and the high four bit thermometer code are segmented.The next step is to 8 bit high speed high precision current steering DAC modules for the specific design,this design adopts SMIC 0.18 m CMOS process of the whole circuit.Can be divided into two parts:analog and digital,analog part includes a bandgap reference circuit,voltage to current circuit,bias voltage generating circuit and a cascode current source and low swing low cross point circuit;digital thermometer includes decoding circuit,latch,buffer,differential switch array.The function of each module and various non ideal factors are analyzed.In the design of specific modules,the structure that can reduce the non ideal factors is adopted.For example,the common source cascade current source structure rather than a single current source;the differential structure of the switch instead of single switch;the latch and buffer to eliminate the delay caused by the clock synchronization;structure optimization of cascode type switch will switch the traditional structure,to reduce the effect of voltage fluctuation on the output switch the end of the.Finally,the whole circuit is simulated and the layout is designed.The Cadence Spectre tool is used to simulate the circuit.The differential nonlinearity(DNL)of ADC is less than 0.2LSB,and the integral nonlinearity(INL)is less than 0.4LSB,The spurious dynamic range(SFDR)is less than-60dB.The simulation results show that the circuit has good static and dynamic performance.The layout design part mainly uses Cadence Layout and Calibre tools for layout design.