Analyses of parasitic capacitance effects and flicker noise of the DAC capacitor array for high resolution SAR ADCs

Copyright © 2018 Inderscience Enterprises Ltd. This paper analyses the effects of parasitic capacitances of unit capacitors on the accuracy and the noise performance of the DAC capacitor array in a SAR ADC, showing that thermal noise of the array decreases while gain error is introduced. The gain error is almost independent of the number of bits, but the dynamic range of the high resolution ADC is severely reduced due to the gain error. The post-layout parasitic capacitance analysis of a 10-bit poly-poly array shows a large difference between the top-plate and bottom-plate parasitic capacitances so that the gain error can be decreased by 152 times when top-plates are connected together as the output node of the array. The switching transistors’ flicker noise calculation for a 10-bit and an 18-bit SAR ADC shows that flicker noise can be safely ignored for 10-bit 1MSPS SAR, but should be considered for the higher resolution SAR ADCs

Charge-based supercapacitor storage estimation for indoor sub-mW photovoltaic energy harvesting powered wireless sensor nodes

Supercapacitors offer an attractive energy storage solution for lifetime “fit and forget” photovoltaic (PV) energy harvesting powered wireless sensor nodes for internet of things (IoT) applications. Whilst their low storage capacity is not an issue for sub-mW PV applications, energy loss in the charge redistribution process is a concern. Currently there is no effective method to estimate the storage of the supercapacitor in IoT applications for optimal performance with sub-mW input. The existing energy-based method requires supercapacitor model parameters to be obtained and the initial charge state to be determined, consequently it is not suitable for practical applications. This paper defines a charge-based method, which can directly evaluate supercapacitor’s storage with straightforward calculations. Time constant analysis and experimental tests demonstrate that with the newly proposed method the manufacturer-specified tiny leakage current, although measured long after post-charge (e.g. 72 hours), can be directly used, making the storage estimation for a supercapacitor in IoT applications as simple as that for an ordinary capacitor. In addition, the demonstrated tiny leakage current at the required energy storage for a sub-mW PV powered IoT application enables a supercapacitor alone to be employed as the storage mechanism, thus achieving lifetime battery-replacementfree, self-powered IoT nodes

Trajectory tracking of a quadrotor using extend state observer based U-model enhanced double sliding mode control

This paper develops a novel U-model enhanced double sliding mode controller (UDSMC) for a quadrotor based on multiple-input and multiple-output extended-state-observer (MIMO-ESO). UDSMC is designed using Lyapunov synthesis and Hurwitz stability to not only cancel the complex dynamics and nonlinearity, but also stabilize the uncertainty and external disturbance of the underlying quadrotors. MIMO-ESO is designed to estimate the unmeasurable velocities which can reduce the impact of sensor measurement errors in practice. The difficulties associated with quadrotor velocity's measurement disturbances and uncertain aerodynamics are successfully addressed in this control design. Rigorous theoretical analysis has been carried out to determine whether the proposed control system can achieve stable trajectory tracking performance, and a comparative real-time experimental study has also been carried out to verify the better effectiveness of the proposed control system than the built-in PID control system

Adaptive sliding mode attitude control of 2-degrees-of-freedom helicopter system with actuator saturation and disturbances

The modelling uncertainties, external disturbance and actuator saturation issues will degrade the performance and even the safety of flight. To improve control performance, this study proposes an adaptive U-model based double sliding control (UDSMC) algorithm combined with a radial basis function neural network (RBFNN) for a nonlinear two-degrees-of-freedom (2-DOF) helicopter system. Firstly, the adaptive RBFNN is designed to approximate the system dynamics with unknown uncertainties. Furthermore, two adaptive laws are designed to deal with unknown external disturbances and actuator saturation errors. The global stability of the proposed helicopter control system is rigorously guaranteed by the Lyapunov stability analysis, realizing precise attitude tracking control. Finally, the comparative experiments with conventional SMC and adaptive SMC algorithms conducted on the Quanser Aero2 platform demonstrate the effectiveness and feasibility of the proposed 2-DOF helicopter control algorithm

Passive impedance sensing using a SAW resonator-coupled biosensor for zero-power wearable applications

A bio-sensing scheme, which acquires impedance information of a capacitive biosensor by using the reflected RF signal from a surface acoustic wave (SAW) resonator connected to the biosensor, is proposed. This technique requires no power to be supplied to the biosensor node and hence is highly applicable to wearable applications. Theoretical analysis has demonstrated that the sensitivity of the SAW resonator-coupled biosensor is higher than that of traditional impedance loaded SAW sensors and therefore it is more suitable for measuring the very small impedance changes in biosensors. The passive detection of the change in the impedance of a capacitive biosensor, as a result of biological binding events associated with the capture of a target analyte, has been demonstrated by preliminary experimentation. Dry tests of the SAW coupled capacitive biosensor using a cable connected network analyzer showed the aF level capacitance measurement resolution, which was only achieved in transistor level circuits previously, could be attained. When liquid samples with concentrations of C-Reactive Protein (CRP) in the range of 0.1 to 2 μg/ml were applied to the biosensor, a corresponding change in the resonant frequency of the SAW resonator-coupled biosensor (in the order of sub-hundred kHz) was observed. This has demonstrated the potential for applying this technique in applications where a zero-power requirement at the biosensor node could be a distinct advantage, when the cable link between the network analyzer and the biosensor node is replaced by the RF transmission

An implantable mixed-signal CMOS die for battery-powered in vivo blowfly neural recordings

© 2018 A mixed-signal die containing two differential input amplifiers, a multiplexer and a 50 KSPS, 10-bit SAR ADC, has been designed and fabricated in a 0.35 μm CMOS process for in vivo neural recording from freely moving blowflies where power supplied voltage drops quickly due to the space/weight limited insufficient capacity of the battery. The designed neural amplifier has a 66 + dB gain, 0.13 Hz-5.3 KHz bandwidth and 0.39% THD. A 20% power supply voltage drop causes only a 3% change in amplifier gain and 0.9-bit resolution degrading for SAR ADC while the on-chip data modulation reduces the chip size, rendering the designed chip suitable for battery-powered applications. The fabricated die occupies 1.1 mm2 while consuming 238 μW, being suitable for implantable neural recordings from insects as small as a blowfly for electrophysiological studies of their sensorimotor control mechanisms. The functionality of the die has been validated by recording the signals from identified interneurons in the blowfly visual system

Determining the reliable minimum unit capacitance for the DAC capacitor array of SAR ADCs

The layout area of an SAR ADC is mainly occupied by its DAC capacitor array. Since there are 2 matched unit capacitors employed for a binary-weighted N-bit DAC, selecting a small unit capacitance is the key to reducing the layout area of the capacitor array, and accordingly reduce the total area of an SAR ADC for size-constrained implantable or wearable applications. In this paper the matching error and thermal noise of the capacitor array are considered systematically for the whole SAR ADC to determine the minimum unit capacitance. The statistical analysis shows that the matching error of the capacitor array depends not only on the matching parameter of the given process but also on the confidence level of the design, while thermal noise analysis shows that thermal noise of the capacitor array does not equal that of either the unit capacitor or the total capacitance of the capacitor array. The calculations for the matching error and thermal noise of a 10-bit DAC show that although the matching error is 7 times bigger, thermal noise which consumes 1/8 error budget should not be ignored for determining the reliable minimum unit capacitance. An iterative algorithm is proposed to find the minimum value when both matching error and thermal noise are considered. A 10-bit SAR ADC adopting an 89.44 fF poly-poly unit capacitor in the 0.35 μm CMOS process validated the method

FPGA design and implementation for EIT data acquisition

OXBACT-5 was designed to meet the challenges involved in working in the intensive care hospital environment focussed particularly on thoracic imaging of patients with respiratory distress and chronic heart failure (CHF). The FPGA-based wireless LAN linked multi-channel EIT data acquisition system (DAS) providing 16 programmable excitation current channels and 64 voltage measurement channels is presented. It contains function modules of a PCI bus interface, direct digital synthesizers, dual-port memory blocks, digital demodulation and all the command and control logic in the FPGA. The whole EIT data acquisition system is fully programmable and reconfigurable from the host PC. The excitation frequency, excitation patterns, the measuring sequence and the gain of each measurement channel can be set from the host PC before each measurement. The demodulation is implemented in the FPGA chip to reduce the data rate between the DAS and the host PC. In addition, measurement process management is achieved in this FPGA chip. Complemented by analogue devices such as ADCs, DACs, analogue buffers and analogue multiplexers, the new FPGA-based EIT DAS system is implemented in a very compact way for bedside use in intensive care units of hospitals. It is intended for applications such as continuous respiration monitoring with data collection at 25 frames per second. Image reconstruction times depend on the choice of 2D or 3D imaging algorithms and the available processing power. © 2008 Institute of Physics and Engineering in Medicine

Does price limit affect the autocorrelation of stock return series? A Monte Carlo experiment

This paper explores whether the regulation of price limits in financial markets will result in the autocorrelation of stock return series. The results of Monte Carlo Experiment under different error term distribution hypothesis suggest that such price limit mechanism will result in a positive first-order autocorrelation of return series. The results indicates that some statistics in empirical finance literature for testing random walk or market efficiency, for example, the variance ratio of Lo and MacKinlay(1988), may be biased when the stock price is subject to the price limit. This paper also suggests that the further research on the price limit is necessary when more exchanges adopt such regulations in the world

Neural networks for improved text-independent speaker identification

In this article, we consider the binary partitioned approach with pattern index information, propose an neural network array (NNA) that performs the pattern recognition task by combining the binary partitioned approach with decision trees, and verify that the NNA can not only reduce the computation cost of training and recognition but also reduce the classification error rate. Speaker identification with the radial basis function neural network array (RBFNNA) is discussed in detail as an application of the NNA