Using Orthogonal Sequences in "blind" Calibration of an Array of Analog-to-digitalconverters

Fig. 1 N-path Time-interleaved ADC • In this paper, we propose a new calibration scheme suitable forimproving the fidelity of data-conversion in an array of ADCs, which is otherwise degraded largely due to mismatches in the non-ideaI behaviours among the individuaI ADCs in the array. This work will focus on correcting the ill-effects suffered by the array of ADCs due to mismatches in gain and offset errors of the individuaI ADCs. In order to quantify the improvement achieved using the proposed calibration scheme, a Time-interleaved ADC (N-channeVpath case shown in fig. I) is taken as a case study, with the signal-distortion at its output, expressed as Spurious Free Dynamic Range (SFDR), being the quantity used to measure the improvement. However, the proposed calibration scheme is equally applicable for any array of ADCs where fidelity of data-conversion is limited Iargely by the mismatches in the gain and offset errors among individuaI ADCs in the array. The organization of this paper is as follows. Section 2 provides a window to the currently existing literature on the subject. In Section 3, the calibration scheme is evolved by starting with an observation of the utility of orthogonal sequences in certain spreadspectrum techniques like Code Division Multiple Access (CDMA). This section also explains the advantages ofthe proposed scheme relative to some curl. INTRODUCTION AND OVERVIEW IO/h IMEKO.TC7 Internattonal Symposium June 30-Ju/y 2, 2004, Saint-Petersburg, Russia