Research And Design Of 16-Bit 200-MS/s Current-steering DAC

With the rapid development of electronics and the wide application of computers in automation,it has become more common to use digital systems to process signals,and digital to analog converter(DAC)which connects nature and digital systems,plays an essential role.In order to meet the requirements of high-speed and high-precision DAC,the DACs with different structures is analyzed and compared in the thesis.Then the current-steering structure is determined.For the input digital signal,the current signal corresponding to the size of the digital signal is sent to the output.Then a voltage is generated on the corresponding load,and the conversion of the digital signal to the analog signal is completed by the DAC.The high-speed and high-precision DAC includes segmented decoder,switch driving circuit,low-voltage bandgap reference voltage source,voltage-to-current circuit,bias circuit of current source,current source and switch array and digital foreground self-calibration,etc.Since the performance of the current-steering DAC is affected by the decoding method,after analysis,a segmented decoding structure of 5+5+6 is adopted,in which the high five bits and the middle five bits are decoded by thermometer,and the low six bits are decoded by binary.The performance of current-steering DAC can be improved by this structure.And the decoding circuit is optimized to improve the linearity of the circuit.The glitch at the output of the DAC will be caused by the parasitic effect of the switch and the asymmetrical cross point of the switching control signal.To suppress this phenomenon,a virtual switch and a switch driving circuit for reducing the swing and cross point of the switch control signal are designed,which improves the performance of the DAC.The high-speed and high-precision current-steering DAC has high requirements on the accuracy and matching of the current source.For this reason,a current source bias circuit with high stability and high output swing is designed,which can improve the current replication accuracy;a cascode structure is adopted to improve the output impedance of the current source;finally,a digital foreground self-calibration technique is proposed,which can compensate the error of the current source and improve the dynamic performance of the DAC.The 16-bit 200-MS/s current-steering DAC designed in this thesis is based on 40 nm CMOS process,powered by a1.1V/1.8V dual supply voltage,with a layout area of approximately 1.16 mm~2.The post-simulation results show that DNL is 0.23 LSB and INL is 0.40 LSB when the sampling clock frequency is 200MHz,and the spurious-free dynamic range is above 80 d B with calibration in the Nyquist band,which meet the design requirements.The high-speed and high-precision DAC designed in this thesis is qualified with engineering application value.It can be widely used in the field of communication.In fiber optic communication,high performance DAC is needed at the transmitter of the signal.In the military field,ultra-high-speed DAC is an important device for radar.In some special fields,high-speed and high-precision DAC is needed for high-precision medical instruments and test instruments.