A High-Linearity Pipelined ADC With Opamp Split-Sharing in a Combined Front-End of S/H and MDAC1

This paper presents a power-efficient, high-linearity pipelined ADC, utilizing a combined front-end of the sample/hold circuit (S/H) and the first multiplying digital-to-analog converter (MDAC1). In contrast with the conventional merged sample-and-hold amplifier (SHA) and first MDAC, the front-end uses an opamp split-sharing scheme to meet the different gain and bandwidth requirements of both the S/H and the first MDAC. This opamp split-sharing scheme mitigates the memory effect without a dedicated clock phase and avoids crosstalk. In the back-end ADC, 4.5-bit opamp-sharing MDACs with four-input operational trans-conductance amplifiers (OTAs) are used for further power saving. Implemented in a 0.18-μm CMOS process, the 14-bit ADC achieves a spurious-free dynamic range (SFDR) of 89.1 dB and a signal-to-noise plus distortion ratio (SNDR) of 70.2 dB, with a sampling rate of 100 MS/s and an input of 15.5 MHz. For input signals up to 220 MHz, measured SFDR and SNDR are maintained above 82.7 dB and 66.2 dB, respectively. The ADC consumes 92 mW with a 1.8-V supply, occupying an area of 6.3 mm².