New sampling method to improve the SFDR of time-interleaved ADCs

Modern communication systems need high-speed ADCs with wide spurious-free dynamic range (SFDR). Conventional time-interleaved ADCs suffer from spurious components that seriously affect the SFDR. Improvement in the SFDR has been achieved by randomizing the samples of the analog input between the different ADC channels at the expense of adding more ADCs and more analog circuitry to the architecture, which increases the complexity of the system as a whole. In this paper, we present the mathematical background describing the effect of randomizing the samples among the interleaved ADCs and we propose a digitally oriented method, based on this analysis, to randomize the mismatches among the ADC channels. Analysis and behavioral simulations show the effectiveness of the proposed approach in multi-channel ADCs with arbitrary bit resolution and sampling rate. For a 10 bit 500 MS/sec ADC, the SFDR achieved using the proposed randomizing method can be as wide as -79 dBc, which is an enhancement of more than 30 dB compared to the conventional time interleaved ADC.