Udaykiran Eduri, Franco Maloberti
USING ORTHOGONAL SEQUENCES IN ""BLIND"" CALIBRATION OF AN ARRAY OF ANALOG-TO-DIGITAL CONVERTERS
Mismatches in errors between the individual ADCs, more than the errors themselves, have been known to be the dominating cause of signal-distortion in certain systems like a Time-interleaved ADC, implemented using an array of ADCs. A new technique, using orthogonal sequences for effectively eliminating these mismatches, has been proposed in this paper as a scheme suitable for calibrating such an array of ADCs. Ease of implementation compared to currently existing techniques is the main advantage of this new scheme. Online calibration can be performed at the expense of some circuit overhead involving one additional ADC as a reference ADC, switches, DSP and memory, while offline calibration does not require the additional ADC, since any particular ADC in the array may be used as the reference. The reduction in signal-distortion for different resolutions of the reference ADC has been substantiated through simulations performed on a modelled 4-path Time-interleaved ADC. When all the ADCs have been modelled with 12-bit resolution and with up to 1% offset error and 5% gain error, the improvement in SFDR achieved using this calibration scheme is up to 54 dB.
