Radix-based digital calibration technique for multi-stage ADC

This paper describes a digital-domain self-calibration technique for a multi-stage analog-to-digital converter (ADC). An accurate calibration is achieved by using a modified radix-based calculation. The equivalent radix-based error term for each stage is extracted by measuring major carry jumps from the ADC transfer curve. A new multiplying digital-to-analog converter (MDAC) architecture using V_ref/2 (instead of V_ref) is used to reduce the number of error terms in each stage. The radix-based digital calibration technique calibrates capacitor mismatch as well as finite opamp DC gain, while the digital redundancy compensates for opamp and comparator offsets and signal-independent charge injection.