A digital background calibration method for time-interleaved ADCs based on frequency shifting technique

The presence of channel mismatches in time-interleaved analog-to-digital converters (TIADCs) seriously degrades the performance of the acquisition system. This paper presents a digital background calibration method to address gain and time skew mismatches. The spurious signals caused by gain and time skew mismatches can be represented by the frequency-shifted signals produced by modulating the TIADC output. To create frequency-shifted signals, the Hadamard transform is adopted. The advantage of the proposed calibration method is that it does not require any filters or complex signal processing structures, thus considerably decreasing the complexity of the calibration circuit. We have employed a four-channel TIADC system to validate the effectiveness of the proposed calibration technique. Moreover, it is demonstrated in a commercial 12.5 GSPS four-channel TIADC system, that this method improves the spurious free dynamic range of the system by 25 dB.