一個具備數位背景式校正機制之十三位元每秒一億次取樣0.18-um CMOS導管式類比數位轉換器的設計

Abstract

In the front-end of a conventional pipelined ADC, the embedded multiplying digital-to-analog converter (MDAC) has to meet very stringent noise, speed, and linearity requirements. As a result, the MDAC needs an operational amplifier (OP) with a very high open-loop gain and a large unity-gain bandwidth. Such an OP dominates the overall power dissipation of the pipelined ADC. Moreover, as the advanced technology keeps scaling, the reduced supply voltage limits the signal headroom and the reduced channel length decreases the intrinsic gain of transistors.Consequently, it is very difficult to design an OP that can achieve the stringent specifications with the advanced technology. In order to save power and alleviate the design difficulty in advanced technology,this thesis proposes a 13-bit 100-MS/s pipelined ADC with digital background calibration. The design replaces the conventional closed-loop residue amplifier with a simple open-loop architecture in the first pipelined stage which specifications is the most stringent in the pipelined ADC. The gain error and the third-order nonlinearity of the open-loop residue amplifier are calibrated using a digital background calibration technique. The calibration scheme continuously estimates and calibrates the errors introduced by the imprecise and nonlinear gain of the open-loop residue amplifier. By adopting the concept of digital-assist analog circuit design, this thesis implements a high performance pipelined ADC with the aid of CMOS scaling. The proposed pipelined ADC has been designed and fabricated in a TSMC 0.18-um CMOS process and the digital background calibration is implemented by a FPGA. The measurement results show that the ENOBs of the ADC output with calibration and without calibration at an analog power supply of 1.65V, a digital power supply of 1.8V, and a sampling rate of 12MS/s are 5.3 bits and 7.2 bits,respectively. There are two possible reasons that cause the performance degradation of the pipelined ADC. First, the pipelined ADC can’t work properly and the offset of the backend stage can’t be cancelled because of a timing error of the comparator design. Second, the operating speed of the flash memory on the FPGA board limits the sampling rate of the pipelined ADC to be less than 12MS/s.