287 research outputs found
Robustness Enhancement in Neural Networks with Alpha-Stable Training Noise
With the increasing use of deep learning on data collected by non-perfect
sensors and in non-perfect environments, the robustness of deep learning
systems has become an important issue. A common approach for obtaining
robustness to noise has been to train deep learning systems with data augmented
with Gaussian noise. In this work, we challenge the common choice of Gaussian
noise and explore the possibility of stronger robustness for non-Gaussian
impulsive noise, specifically alpha-stable noise. Justified by the Generalized
Central Limit Theorem and evidenced by observations in various application
areas, alpha-stable noise is widely present in nature. By comparing the testing
accuracy of models trained with Gaussian noise and alpha-stable noise on data
corrupted by different noise, we find that training with alpha-stable noise is
more effective than Gaussian noise, especially when the dataset is corrupted by
impulsive noise, thus improving the robustness of the model. The generality of
this conclusion is validated through experiments conducted on various deep
learning models with image and time series datasets, and other benchmark
corrupted datasets. Consequently, we propose a novel data augmentation method
that replaces Gaussian noise, which is typically added to the training data,
with alpha-stable noise
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Accuracy enhancement techniques in low-voltage high-speed pipelined ADC design
Pipelined analog to digital converters (ADCs) are very important building blocks in many electronic systems such as high quality video systems, high performance digital communication systems and high speed data acquisition systems. The rapid development of these applications is driving the design of pipeline ADCs towards higher speed, higher dynamic range, lower power consumption and lower power supply voltage with the CMOS technology scaling. This trend poses great challenges to conventional pipelined ADC designs which rely on high-gain operational amplifiers (opamps) and well matched capacitors to achieve high accuracy. In this thesis, two novel accuracy improvement techniques to overcome the accuracy limit set by analog building blocks (opamps and capacitors) in the context of low-voltage and high-speed pipelined ADC design are presented. One is the time-shifted correlated double sampling (CDS) technique which addresses the finite opamp gain effect and the other is the radix-based background digital calibration technique which can take care of both finite opamp gain and capacitor mismatch. These methods are simple, easy to implement and power efficient. The effectiveness of the proposed techniques is demonstrated in simulation as well as in experiment. Two prototype ADCs have been designed and fabricated in 0.18μm CMOS technology as the experimental verification of the proposed techniques. The first ADC is a 1.8V 10-bit pipeline ADC which incorporated the time-shifted CDS technique to boost the effective gain of the amplifiers. Much better gain-bandwidth tradeoff in amplifier design is achieved with this gain boosting. Measurement results show total power consumption of 67mW at 1.8V when operating at 100MSPS. The SNR, SNDR and SFDR are 55dB, 54dB and 65dB respectively given a 1MHz input signal. The second one is a 0.9V 12-bit two-stage cyclic ADC which employed a novel correlation-based background calibration to enhance the linearity. The linearity limit set by the capacitor mismatches, finite opamp gain effects is exceeded. After calibration, the SFDR is improved by about 33dB and exceeds 80dB. The power consumption is 12mW from 0.9V supply when operating at 2MSPS
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