A new orthogonal online digital calibration for time-interleaved analog-to-digital converters

Modern communication technologies need faster analog- to-digital converters (ADC). To significantly increase the sampling rate of an ADC, time-interleaved ADC (TIADC) is an efficient solution. A M-channels TIADC is composed of M ADCs which operate at interleaved sampling times. Due to the manufacturing process, the main drawback of a TIADC system is that the MADCs are not exactly the same. This means that offset, gain and time mismatch errors are introduced. As a result, these errors cause distortions in the output sampled signal and introduce unwanted tones and noise, and hence, reduce the spurious free dynamic range (SFDR) as well as the signal to noise ratio (SNR). In this paper, we propose a new orthogonal online digital calibration, for timing skew, offset and gain mismatches, based on Code Division Multiple Access (CDMA) technique already used in communications. Our calibration is online, this means that errors can be estimated while the ADC is running. Since most of the calibration processes are carried out on the digital outputs, very little change is needed on the analog part of the ADC. Simulations results showed the efficiency of our proposed calibration architecture.