Digital mismatch correction for bandpass sampling four-channel time-interleaved ADCs in Direct-RF sampling receivers

Abstract

Time-interleaving analog-to-digital converters (ADCs) decrease the required sampling rate for one ADC to achieve giga samples per second (GS/s) rates. The gain and timing mismatches among the ADCs generate aliasing signals, degrading the spurious-free dynamic range of the time-interleaved ADC (TI-ADC). The conventional digital correction methods for TI-ADCs have not considered an application to direct-radio-frequency (RF) sampling receivers. We present a digital correction method for bandpass sampling four-channel TI-ADCs in the receivers. The proposed method, based on a correction method for two-channel TI-ADCs, reduces the in-band aliasing signals of the four-channel TI-ADCs by using in-phase/quadrature-phase (I/Q) downconversion mixers, cascaded integrator-comb (CIC) filters, and automatic gain control (AGC) in the receiver. This allows the correction circuit including mismatch estimation to have fewer building blocks than the conventional methods: seven adders, seven multipliers, and no finite-impulse-response filters. Simulations and measurements show that the proposed method reduces the aliasing signals of 1.2 GS/s 12-bit four-channel TI-ADCs to less than -80 dBFS.