Noise Coupling Technique Research Articles

A multi-stage sigma-delta modulator based on noise-coupling and digital feed-forward techniques

This paper presents a new structure for high-resolution, low-power and wideband discrete time multi-stage (DT-MASH) sigma-delta (ΣΔ) modulators. It uses multi-bit digital input feed forward path (DFF) and noise coupling (NC) techniques. With the DFF technique, the modulator does not need a power-consuming analog adder at the quantizer input, and the number of comparators of the quantizer will be reduced significantly. Also, because of the reduced swing of the modulator’s integrators, low power integrators can be used. Using a second-order NC technique with no extra active block, the order of the modulator, which uses some paths between analog stages, is increased, and its performance is improved with zero-optimization of the modulator’s noise transfer function (NTF). Behavioral simulations and extensive mathematical analyses confirm the effectiveness of the proposed structure. The effect of the non-idealities in the DFF and NC paths were considered in the behavioral simulations. To examine its performance, a MASH 2–1 modulator was designed in the circuit level with a 180-nm CMOS technology and 1.8 V power supply. The integrators use a new op-amp switching technique to reduce total power consumption. With an over-sampling ratio (OSR) of 8 for the 10 MHz signal bandwidth, the proposed structure improves the signal-to-noise and distortion ratio (SNDR) by 28 dB compared with a conventional MASH 2–1 structure at approximately the same power consumption and very low complexity.

A second-order continuous-time delta-sigma modulator with double self noise coupling

In this paper, a second-order continuous-time delta-sigma modulator using double self noise coupling technique is proposed. Noise coupling increases the effective order of the noise shaping loops. The presented architecture splits the outputs of the quantizer into a most significant bit segment (MSBs) and a least significant bit segment (LSBs). The LSBs can be viewed as the residue after the MSBs quantization and is fed back to the front of the quantizer and the second integrator respectively, as a result, double self noise coupling is achieved. In addition, the quantizer also provides a convenient means to incorporate the excess-loop-delay compensation. As a result, the digital noise cancellation logic complexity is simplified, the digital and analog filter mismatch is relaxed, meanwhile, it strictly suppresses the noise within the effective signal bandwidth by reducing the main MSBs mismatch. Finally, the resolution is increased, the hardware complexity and the output swing of the integrator are reduced, which greatly relaxes the bandwidth and gain requirement of the Op-Amp design. The higher order noise shaping introduced by the residue of multi-bit quantizer further reduces the quantization noise.

Digital Noise Coupled MASH Delta-Sigma Modulator

This brief proposes digital noise coupling technique for multistage noise shaping Delta–Sigma modulator. In the proposed technique, the digital output of the second stage is fed to the input of the first stage quantizer with unit delay. After digital post-processing, the quantization noise of the first stage will be cancelled. The leaked quantization noise, caused by the mismatch between the analog and digital noise transfer functions, will be shaped by digital coupling. Hence, more robustness to circuit nonidealities such as the finite gain of amplifiers will be achieved, which is appropriate for low power and low voltage applications. Simulation results show the effectiveness of the proposed architecture.

Accuracy and convergence of coupled finite-volume/Monte Carlo codes for plasma edge simulations of nuclear fusion reactors

The plasma and neutral transport in the plasma edge of a nuclear fusion reactor is usually simulated using coupled finite volume (FV)/Monte Carlo (MC) codes. However, under conditions of future reactors like ITER and DEMO, convergence issues become apparent. This paper examines the convergence behaviour and the numerical error contributions with a simplified FV/MC model for three coupling techniques: Correlated Sampling, Random Noise and Robbins Monro. Also, practical procedures to estimate the errors in complex codes are proposed. Moreover, first results with more complex models show that an order of magnitude speedup can be achieved without any loss in accuracy by making use of averaging in the Random Noise coupling technique.

An NTF-enhanced time-based continuous-time sigma-delta modulator

Translation of the amplitude axis to the time axis can be a promising approach to alleviate the analog-to-digital converter's resolution problems in low-voltage CMOS circuits. From this point of view, a noise-coupled time-based continuous-time sigma-delta modulator (TCSDM) based on the asynchronous pulse width modulator (APWM) and the time-to-digital converter (TDC) is presented. Noise-coupling is realized by extracting the time quantization error of the TDC and injecting its delayed version to the input of the APWM. By using a novel implementation of the noise-coupling technique in the proposed TCSDM, the modulator's noise-shaping order is improved by one. Unlike the conventional noise-coupled sigma-delta modulators, in the proposed structure, the need of an extra subtractor at the quantizer input is resolved through merging the excess loop delay compensation path with the proposed noise-coupling branch. Comparative analytical calculations and behavioral simulation results are presented to verify the performance of the proposed time-based modulator. To confirm the validity of the proposed structure, the effects of main circuit non-idealities in the modulator's performance are taken into consideration and the related simulation results are investigated. A digital-friendly implementation of the quantizer in the proposed modulator makes it suitable for low-voltage nanometer CMOS technologies.

Filter Loop Reduction in DT BP Sigma-Delta Modulator Assisted by Noise Coupling Technique

In bandpass modulators, a 2N-order loop filter can lead to an N-order noise shaping in the band of interest. This caused a bandpass modulator with more complex structure than a lowpass modulator and increased the power consumption and area of the modulator. In this paper, we proposed a discrete-time bandpass modulator using the noise-coupling technique that only needs to a second- order loop filter to have a second-order noise shaping. To realize a noise coupled bandpass modulator, we need to implement Z -2 delay block in the analog domain, but the proposed modulator uses only Z -1 delay blocks to apply the noise coupling technique. This simplifies the structure of the modulator and reduces the power consumption, area, and nonlinearity of the modulator. The error in the coupling path is considered and the effect of it on the modulator resolution is analyzed. According to the simulation results, the proposed modulator results in SNR = 84.9 dB at 80 MHz sampling frequency, 200 KHz bandwidth and OSR = 200.

Digital Noise-Coupling Technique for Delta–Sigma Modulators With Segmented Quantization

A digital noise-coupling technique for delta–sigma modulators with a high-resolution quantizer is presented. The proposed technique divides the outputs of the quantizer into an MSB segment and an LSB segment. The MSBs are directly fed to the modulator input, whereas the LSBs are used as the quantization noise for noise coupling. After the digital postprocessing, the MSBs and the LSBs are then recombined. As a result, it preserves the benefit of increased quantization levels without suffering from the exponential growth of the dynamic element matching logic. The extra noise shaping introduced by the LSB feedback further reduces the quantization noise leakage caused by the mismatch between the analog and digital noise transfer functions, which allows a more relaxed operational amplifier design. This technique is simple to implement and well suited for low-power and wideband applications.

A time-domain noise-coupling technique for continuous-time sigma-delta modulators

In this paper, a time-domain noise-coupling technique based on the pulse width modulation is proposed. The time-domain quantization error is digitally extracted and shaped by an asynchronous digital filter. This digitally filtered quantization error is applied to the quantizer input to increase the modulator's noise-shaping order. By using this technique in continuous-time sigma-delta modulators, the modulator's shaping property is significantly enhanced. Comparative analytical calculations and simulation results are presented to estimate the performance of modulators employing the proposed quantizer. System-level simulation results reveal a (L + 2)th order noise-shaping capability of the proposed modulator while it employs only L analog integrators. The effects of main circuit non-idealities in the modulator's performance are analytically investigated and confirmed by the simulation results.

Noise-coupled continuous-time delta-sigma ADCs

The noise-coupling technique successfully used in discrete-time delta-sigma analogue-to-digital converters (ADCs) is extended to the realisation of continuous-time delta-sigma ADCs, resulting in improved quantisation noise shaping. To verify the proposed design methodology, a second-order continuous-time delta-sigma modulator with noise coupling is designed and simulated.