A time-interleaved A-D converter (ADC) system is an effective way to implement a high-sampling-rate ADC with relatively slow circuits. In the system, several channel ADCs operate at interleaved sampling times as if they were effectively a single ADC operating at a much higher sampling rate. However, mismatches such as offset, gain mismatches among channel ADCs as well as timing skew of the clocks distributed to them degrade S/N of the ADC system as a whole. This paper analyzes the channel mismatch effects in the time-interleaved ADC system. Previous analysis showed the effect for each mismatch individually, however in this paper we derive explicit formulas for the mismatch effects when all of offset, gain and timing mismatches exist together. We have clarified that the gain and timing mismatch effects interact with each other but the offset mismatch effect is independent from them, and this can be seen clearly in frequency domain. We also discuss the bandwidth mismatch effect. The derived formulas can be used for calibration algorithms to compensate for the channel mismatch effects.

/pdf/explicit-analysis-of-channel-mismatch-effects-in-time-35iix1n2s2.pdf

Explicit analysis of channel mismatch effects in time-interleaved ADC systems

Digital calibration using adaptive signal processing corrects for offset mismatch, gain mismatch, and sample-time error between time-interleaved channels in a 10-b 120-Msample/s pipelined analog-to-digital converter (ADC). Offset mismatch between channels is overcome with a random chopper-based offset calibration. Gain mismatch and sample-time error are overcome with correlation-based algorithms, which drive the correlation between a signal and its chopped image or its chopped and delayed image to zero. Test results show that, with a 0.99-MHz sinusoidal input, the ADC achieves a peak signal-to-noise-and-distortion ratio (SNDR) of 56.8 dB, a peak integral nonlinearity of 0.88 least significant bit (LSB), and a peak differential nonlinearity of 0.44 LSB. For a 39.9-MHz sinusoidal input, the ADC achieves a peak SNDR of 50.2 dB. The active area is 5.2 mm/sup 2/, and the power dissipation is 234 mW from a 3.3-V supply.

A 10b 120MSample/s time-interleaved analog-to-digital converter with digital background calibration

Interleaving can relax the power-speed tradeoffs of analog-to-digital converters and reduce their metastability error rate while increasing the input capacitance. This paper quantifies the benefits and derives an upper bound on the performance by considering kT/C noise and slewing requirements of the circuit driving the system. A frequency-domain analysis of interleaved converters is also presented that sheds light on the corruption mechanisms due to interchannel mismatches. A background timing mismatch calibration technique is proposed and experimentally shown to reduce the image to -75 dB for input frequencies exceeding 500 MHz.

/pdf/design-considerations-for-interleaved-adcs-3nt0r0ms3k.pdf

Design Considerations for Interleaved ADCs

A time-interleaved multichannel analog-to-digital converter (ADC) achieves high sampling rates with the drawback of additional distortions caused by channel mismatches. In this paper, we consider the dependency of the signal-to-noise-and-distortion ratio (SINAD) on the combination of several different channel mismatch effects. By using either explicitly given mismatch parameters or given parameter distributions, we derive closed-form equations for calculating the explicit or the expected SINAD for an arbitrary number of channels. Furthermore, we extend the explicit SINAD by the impact of timing jitter. We clarify how channel mismatches interact and perform a worst case analysis of the explicit SINAD for individual mismatch errors. We also show that equations describing the expected SINAD of individual mismatch errors are special cases of our general formulation. We indicate how to use the expected SINAD for finding efficient optimization priorities and demonstrate the importance of worst case analyses.

/pdf/the-impact-of-combined-channel-mismatch-effects-in-time-46oj642noi.pdf

The impact of combined channel mismatch effects in time-interleaved ADCs

Offset mismatch, gain mismatch, and sample-time error between time-interleaved channels limit the performance of time-interleaved analog-to-digital converters (ADCs). This paper focuses on the sample-time error. Techniques for correcting and detecting sample-time error in a two-channel ADC are described, and simulation results are presented.

Calibration of sample-time error in a two-channel time-interleaved analog-to-digital converter

Sampling clock jitter effects in digital-to-analog converters

A time-interleaved ADC system is an effective way to implement a high-sampling-rate ADC with relatively slow circuits. In the system, several channel ADCs operate at interleaved sampling times as if they were effectively a single ADC operating at a much higher sampling rate. However, mismatches among channel ADCs degrade S/N of the ADC system as a whole, and the effects of offset, gain and bandwidth mismatches as well as timing skew of the clocks distributed to the channels have been well investigated. This paper investigates the channel linearity mismatch effects in the time-interleaved ADC system, which are practically very important but have not been investigated yet. We consider two cases: differential nonlinearity mismatch and integral nonlinearity mismatch cases. Our numerical simulation shows their distinct features especially in frequency domain. The derived results can be useful for calibration algorithms to compensate for the channel mismatch effects.

Channel linearity mismatch effects in time-interleaved ADC systems

A time-interleaved ADC system is an effective way to implement a high-sampling-rate ADC with relatively slow circuits. In the system, several channel ADCs operate at interleaved sampling times as if they were effectively a single ADC operating at a much higher sampling rate. However, mismatches such as offset, gain mismatches among channel ADCs as well as timing skew of the clocks distributed to them degrade S/N of the ADC system as a whole. This paper analyzes the channel mismatch effects in the time-interleaved ADC system. Previous analysis showed the effect for each mismatch individually, however in this paper we derive explicit formula for the mismatch effects when all of offset, gain and timing mismatches exist together. We have clarified that the gain and timing mismatch effects interact each other but the offset mismatch effect is independent from them, and this can be seen clearly in frequency domain. We also discuss the bandwidth mismatch effect. The derived formula can be used for calibration algorithms to compensate for the channel mismatch effects.

Naoki Kurosawa

Papers

Explicit analysis of channel mismatch effects in time-interleaved ADC systems

Sampling clock jitter effects in digital-to-analog converters

Channel linearity mismatch effects in time-interleaved ADC systems

Explicit formula for channel mismatch effects in time-interleaved ADC systems

Channel Linearity Mismatch Effects in Time-Interleaved ADC Systems