Timing Skew Calibration Method for TIADC-Based 20 GSPS Digital Storage Oscilloscope

摘要

Time-interleaved technique is widely used to increase the sampling rate of analog-to-digital converter (ADC). However, the channel mismatches degrade the performance of time-interleaved ADC (TIADC). When input signal frequency is very high, timing skews have significant effect on distortion. Therefore, a new timing skew calibration method is proposed in this paper. This method is based on the truth that timing skews are related to the product of the outputs of sub-ADCs. After timing skews are estimated, the digital controlled delay elements (DCDE) in ADC and phase locked loop (PLL) are utilized to calibrate timing skews. No auxiliary circuit and digital filter are needed for this calibration method. Simulation results show that the proposed method can estimate timing skew accurately. It is also proved that an accurate estimation can be obtained even the signal to noise ratio (SNR) of input signal is 20 dB. The proposed method is employed to calibrate timing skews in a 16-channel TIADC-based 20 GSPS digital storage oscilloscope (DSO). The experiment results demonstrate the usefulness of the proposed method. We can see that after timing skews are calibrated, the spectrum spurs have been effectively eliminated.