Biography
Enrollment Date: 2010
Graduation Date：2013
Degree：M.S.
Defense Date：2013.05.27
Advisors：Fule Li
Department：Institute of Microelectronics，Tsinghua University
Title of Dissertation/Thesis：Design of Current-steering Digital-to-Analog Converters and Corresponding Calibration Method
Abstract:
In recent years, achievements boomed in the fields of digital signal process, media application and communication system. All these systems employ digital-to-analog converters (DAC), whose performance is highly demanded.Conversion network could be built by capacitors, resistors or current sources, among whom current sources are superior in dynamic performance. To trade off between chip area and nonlinearity, segmented current-steering architecture is usually selected. The most significant bits are implemented with unary weights while the least ones with binary weights. Carefully-designed latches should be placed in front of current switches to improve synchronization and to reduce charge feed-through. Centroid switching scheme is useful to degrade system errors. Traditional design method doesn’t employ current calibration. According to process features, accuracy of current is decided by source area. As a result, current sources always occupy most of the chip area. The large source area brings parasitic capacitance and resistance, degrading DAC output-impedance in high frequency domain. This proposes a limitation on dynamic performance of DAC. Calibration methods provide a possible solution to this problem.
This paper introduces three current-steering DACs. 12-bit 400MS/s DAC employs NMOS current sources and 6+2+4 segmentation. Optimized switching scheme and latches are implemented to improve static and dynamic performance. 5mA low-power DAC is an IP on SOC. The designed sample rate is 140MS/s. To reduce chip power, the full scale current decreases to 5mA. Meanwhile, the output voltage range remain the same. Thus higher impedance is needed at the output node. Two cascode transistors are placed on top of each current source. Digital-calibrated DAC employs digital-assisted calibration and 7+4+5 segmentation. Calibration module is composed by controller, error measurement, error quantization and error compensation module.