Cascaded complex ADCs with adaptive digital calibration for I/Q mismatch

Yi Tang, Kuang Wei Cheng, Subhanshu Gupta, Jeyanandh Paramesh, David J. Allstot

Research output: Contribution to journalArticlepeer-review

13 Citations (Scopus)


A complex analog-to-digital converter (ADC) intended for digital intermediate frequency (IF) receiver applications digitizes analog signals at IFs with excellent power/bandwidth efficiency. However, it is vulnerable to mismatches between its in-phase and quadrature (I/Q) paths that can dramatically degrade its performance. The proposed solution mitigates I/Q mismatch effects using a complex sigma-delta (ΣΔ) modulator cascaded with 9-bit pipeline converters in each of the I and Q paths. The quantization noise of the first stage complex modulator is eliminated using an adaptive scheme to calibrate finite-impulse response digital filters in the digital noise-cancellation logic block. Although low-pass ΣΔ cascade ADCs are widely used because of their inherent stability and high-order noise shaping, the complex bandpass cascade architecture introduced herein maintains these advantages and doubles the noise shaping bandwidth. Digital calibration also reduces the effects of analog circuit limitations such as finite operational amplifier gain, which enables high performance and low power consumption with high-speed deep-submicrometer CMOS technology. Behavioral simulations of the complex ΣΔ/pipeline cascade bandpass ADC using the adaptive digital calibration algorithm predict a signal-to-noise ratio (SNR) of 78 dB over a 20-MHz signal bandwidth at a sampling rate of 160 MHz in the presence of a 1% I/Q mismatch.

Original languageEnglish
Pages (from-to)817-827
Number of pages11
JournalIEEE Transactions on Circuits and Systems I: Regular Papers
Issue number3
Publication statusPublished - 2008 Apr

All Science Journal Classification (ASJC) codes

  • Electrical and Electronic Engineering


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