Time-interleaved analog to digital convertor (TIADC) is widely used in engineering to increase the sample rate of acquisition system. However, the mismatches between sub-ADCs in TIADC system result in the distortion of sample output and decrease the sample performance. This paper focuses on the calibration of offset, gain and timing skew mismatches. A novel method based on statistical theory is proposed to estimate offset mismatch of each channel. This method can reduce the impact of noise on offset mismatch calibration. The amplitude of main spectrum is utilized to calibrate gain mismatch, and the average value of each sub-ADC is employed to calibrate timing skew mismatch. Meanwhile, gain mismatch and timing skew mismatch are calibrated by STPNM (Simplified Three Point Newton's method). The proposed calibration method is implemented in a four-channel TIADC based digital storage oscilloscope whose sample rate is 5GSPS. The experiment results show that the impact of mismatches can be reduced effectively and the calibration can be finished in a short time because the convergence is very fast.
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[Formula: see text]dB. The proposed method is employed to calibrate timing skews in a 16-channel TIADC-based 20[Formula: see text]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.
The band interleaved data acquisition system (BI-DAS) is an attractive structure to improve the bandwidth of the acquisition system. However, the non-ideal characteristic of the spectrum analysis filter in BI-DAS results in an overlapping frequency band between two adjacent frequency sub-bands. Phase misalignment (PM) between two sub-bands in the overlapping band may cause those signals canceled or partially canceled to each other when sub-bands' signal are merged. In this paper, a compensation module with a digital all-pass filter (APF) is proposed for the PM of the overlapping bands in BI-DASs. Based on this compensation module, a hybrid Particle Swarm Optimization (PSO) algorithm, along with the Levenberg-Marquardt (LM) algorithm is proposed to design coefficients of the compensation module. The compensation module and corresponding method proposed in this paper are verified in a BI-DAS with 20Gsps sampling rate and 5.5GHz bandwidth. The experimental results show that the proposed compensation module can effectively compensate the PM between the sub-bands in the overlapping band. The proposed hybrid PSO-LM (HPSOLM) algorithm combines the flexibility and reliability inherent in the PSO with the fast convergence and precision of the LM algorithm. It can effectively design the compensation module with stable APF while consuming less time and obtaining better compensation results than the conventional PSO method. INDEX TERMS band interleaved data acquisition system, overlapping band, phase compensation, digital all-pass filters, hybrid Particle Swarm Optimization algorithm, Levenberg-Marquardt algorithm I. INTRODUCTION
TIADC (Time-Interleaved ADC) architecture suffers from errors introduced by mismatches among the interleaved channels, which degrade performance of TIADC significantly. In this paper, a behavioral model for TIADC based on Wiener model is proposed to describe the nonlinearities in TIADC system. The time-domain and frequency-domain representations of the model are derived. Besides, the discrete-time equivalent model is proposed by transforming the hybrid TIADC model to a purely discrete time system, which is useful for the analysis and implementation of subsequent calibration method. What's more, numerous studies have investigated compensation methods for discrete-time Wiener model. The methods in these papers can be modified easily for calibration of TIADC using the model proposed in this paper. The experiment results show the nonlinearities of TIADC in practice are consistent with the model proposed in this paper and simulation results indicates the validity of the proposed discrete-time equivalent model.
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