Design Of A 12-bit Serial Input Dual Output DAC With Digital Calibration

Signal converter acts as the bridge between the digital world and analog world,and deeply infiltrates into communication,sensor,media and other fields of our life.With the popularity of portable equipment like laptop and cellphone,these systems put more stringent requirements on the size,power,performance and other aspects of a signal converter.The author of this paper participated in the design of a 12-bit high precision serial input dual channel DAC product from Chengdu Sino Microelectronics Technology Co.,Ltd.And based on this project,a complete design process is elaborated.This DAC works in the temperature range of-55 ? to 125?,5V-single-supply and 62.5 k Hz sampling rate,with a power consumption of 5 m W,which achieves the main level of domestic military low-power DAC design field.In this paper,first of all,we simply introduce the major standards used to evaluate a DAC,and main DAC structures of nowadays,compare their advantages and weaknesses.In the application scenario where the speed requirement is not high,the R-2R resistor structure becomes the core conversion structure adopted by this design due to the advantages of low component value distribution and small area.Then describe the design flow of every block of this DAC,especially of analog blocks like bandgap reference,bandgap reference's gain block,digital-to-analog conversion block and output operational amplifier.Introduce simulation methods as well as the simulation results of these blocks.Next,to minimize the errors due to the non-ideal effects such as variations in the manufacturing process,we put forward a post-package trimming technique based on digital programmable block.This method allows us to program the EEPROM block inside the chip through the serial input,with which we can reduce the temperature coefficient of bandgap reference and nonlinearity of DAC.Also we can eliminate gain/offset errors of output op-amp and reference's gain block through this method.This trimming method replaces the laser-trim technology adopted by foreign similar chips and the traditional fuse-trim structure adopted in China,breaks through the limitations of foreign trimming technology,reduces product cost,and abandons the disadvantages of high power consumption as well as large area of domestic traditional fuse-trim.On the other hand it will increase the flexibility of trim.At last this paper simply introduce the main problems we may face in the design of mix-signal circuit's layout and the solution of them,emphatically introduce our considerations about the design of key block,DAC resistor arrays.Compare and analysis the advantages and disadvantages of several mainstream package types.By the way we give out the post-package test result of our design with ceramic package.The test result shows that,our design achieve 12-bit resolution perfectly,differential nonlinearity(DNL)and integral nonlinearity(INL)are both limited between-1 and +1 LSB.Besides,the temperature component is lower than 15 ppm/? in the military temperature range(-55~125?).Also,the trimming method used has certain reference value for higherorder DAC circuit design.We offer CSOP-14 plastic and ceramic packages for users to choose from,and replace the similar devices abroad.