Design of high speed Energy Efficient SAR ADC_劉純成.pdf

This dissertation proposes three circuit design techniques for successive-approximation register (SAR) analog-to-digital converters (ADCs). According to the measurement results of the proof-of-concept prototypes, the proposed techniques are able to improve the operating speed and achieve excellent energy efficiency. The proposed techniques and chip measurement results are sketched as follows: The first technique is a monotonic capacitor switching procedure. Compared to converters that use the conventional procedure, the average switching energy and total sampling capacitance are reduced by about 81.3% and 50%, respectively. A 10-bit, 50-MS/s SAR ADC with the proposed monotonic capacitor switching procedure is implemented in a 0.13-μm 1P8M CMOS technology. The prototype ADC consumes 0.92 mW from a 1.2-V supply, and the effective number of bit (ENOB) is 8.48 bits. The resulting figure of merit (FOM) is 52 fJ/conversion-step. However, the signal-dependent offset caused by the variation of the input common-mode voltage degrades the linearity of ADC. We proposed an improved comparator design to avoid the linearity degradation. Besides, to avoid a clock signal with frequency higher than sampling rate, we used an asynchronous control circuit to internally generate the necessary control signals. The revised prototype is also implemented in a 0.13-μm 1P8M CMOS technology. It consumes 0.826 mW from a 1.2-V supply and achieves an ENOB of 9.18 bits. The resultant FOM is 29 fJ/conversion-step.