Digital background calibration of a 0.4-pJ/step 10-bit pipelined ADC without PN generator in 90-nm digital CMOS

In nanometer digital CMOS, the linearity of pipelined A/D converters (ADCs) is degraded by the low dc gains of the opamps. Gain-enhancement techniques significantly increase the analog-circuit design complexity at low power and low voltage. Therefore, even in medium-resolution applications, digital background calibration is attractive for designing power-efficient ADCs. A simple, yet accurate, digital background calibration technique, which does not require a pseudo-random (PN) calibration signal, is proposed to minimize the power dissipation in the digital calibration unit. It achieves the same convergence speed and accuracy as PN-based techniques in 2-path (split) pipelined ADCs. A 10-bit 44-MS/s pipelined ADC, fabricated in a standard 1.2-V 90-nm digital CMOS process, uses the proposed calibration technique to achieve a 58.7-dB SNDR for a 21.5-MHz input, with a figure-of-merit (FOM) of 0.4 pJ/step.