Replica driving technique for switched capacitor circuits & pipelined ADC

Abstract

The proposed replica driving technique reduces power consumption from SC amplifier by separating the output stage into one for accuracy and another for high speed. That is, the amplifier gain accuracy is determined by the closed-loop property while the load is driven rapidly by the open-loop replica stage. By isolating the amplifier from the load capacitor, the amplifier could drive the heavy load capacitor in a power efficient manner. And the proposed replica driving technique is more suitable for heavy capacitive load driving, such as for the front stages of high resolution ADC. The limited signal swing problem of the previous replica driving technique, arising from the source-follower (SF) configured output stage, is resolved through a simple SC level shifter. The output driving capability is ensured by using a class-AB output stage. Owing to the high-speed open-loop output driving, the reference driver does not require any bypass capacitor. Thus, as the load capacitor is increased, the power saving effect of the proposed replica driving technique becomes prominent and suitable for high SNR applications. A prototype 12 bit 200 MS/s pipelined ADC was designed for concept proof in a 65 nm CMOS process. The ADC core which is limited to 150 MS/s consumes 92.4 mW at a 1.2 V supply including reference driver. The measured DNL and INL are 0.5 LSB and 1.5 LSB, respectively. The SNDR and SFDR are 58.2 dB and 73.6 dB at 150 MS/s with an 8.3 MHz input. The main sources of performance degradation are the reduction of gm and the thermal noise of the S/H. The replica driving pipeline ADC is revised from the measurement results. The measured DNL and INL are 0.5 LSB and 1.5 LSB, respectively. The measured SNDR and SFDR are 65.6 dB, 82.6 dB, respectively. At a Nyquist rate input (=99 MHz), they are 58.6 dB and 77.3 dB, respectively. The ADC core and the entire reference drivers consume 53.9 mW and 13.2 mW, respectively, at a 1.2 V supply. The measured results of the revised...