Research Of 12-bit 300MHz DAC For Embedded Use

DAC (Digital-to-Analog Converter, DAC) is a device that change the input digital signal to analog signal output, is widely used in modern communication systems, portable consumer electronics, automotive electronics and other fields, is an indispensable and important building block.With the rapid development of the wireless communications market and mixed-signal products, DAC circuit must require the characteristics of high speed, high resolution, low power and low power consumption, this requirement has become one of Mixed-signal circuit design bottlenecks of the modern communication system.Therefore, The thesis presents the design of a 3.3V 300MS/s 12-bit DAC with embedded applications.This paper introduces the status of digital to analog converter research and development, introducing the basic structure and the basic principles of the DAC,introducing advantages and disadvantages of some typical DACs, analyzing static parameters and the dynamic parameters. Then analyzing the structure of the thermometer code and binary code, considering the chip area and circuit performance and other factors, the paper designs the DAC with the "4+4+4" 12-bit segmented current steering structure, which the 4MSBS and 4MidSBS are thermometer code weighed and 4LSBS are binary weighted. At the same time, analyzing the main factors of limiting the DAC performance, structure are set up behavioral model and simulated by Matlab software, which mainly composes of the thermometer coded, current sources switch driver circuit, bandgap reference and the unit current source array circuit.In the circuit design, the thermometer code controls the unit current source array can reduce the output glitch; In the current source unit, it not only uses cascode structure to increases the output impedance and improves the precision of current source, but also adds the Dummy to restrain the clock feedthrough and charge injection effect; designs a switching control circuit which declines the cross-point and reduce the glitch of output, in order to get a good dynamic performance of DAC; high precision bandgap reference uses Linearization PNP tube compensation and cascade structure, while adding a programmable module, making the output current of reference adjustable. Finally, the paper have completed the whole circuit simulation, mapping and test.This chip is implemented in SMIC 0.35um two polys four metal standard CMOS process, occupies 1.3*1.2 mm2 of die area and power dissipation is 136mW with 3.3V power supply. At 300MHz, DAC spurious-free dynamic range is 64.22dB, differential nonlinearity is 0.3LSB, integral nonlinearity is 0.2LSB for 30MHz input signals, achieving the desired design specifications.