一种2.5Gb/s CMOS宽动态范围光接收机模拟前端电路

基于55nm CMOS工艺,设计了一种具有宽动态范围的2.5Gb/s光接收机模拟前端电路。作为光接收机的输入级电路,为了获得低噪声和高灵敏度性能,跨阻放大器(TIA)基于三级反相器级联结构,同时采用双自动增益控制(DAGC)电路来扩大输入信号的动态范围。为了提高增益,引入后置放大器,包括电平转换电路和三级差分放大电路,同时利用电容简并的方法来进一步拓展带宽,最后进行缓冲器输出。测试结果表明,在误码率为10-12的情况下,光接收机的输入灵敏度为-26dBm,过载光功率为3dBm,动态范围达到29dBm。光接收机在3.3V供电电压下,电流功耗为36mA,整体芯片面积为1176μm×985μm。     

Biomedical microsystems for minimally invasive diagnosis and treatment

Great significant progress has been made in the development of biomedical microdevices in recent years, and these devices are now playing an important role in diagnosis and therapy. This paper presents a review of applications of microelectromechanical systems (MEMS) devices for in vivo diagnosis and therapy, and endoscopic- and catheter-based interventions. MEMS technology has enabled the further development of advanced biomedical microdevices for use in the human body by integration of sensors, actuators, and electronics into small medical devices for use in the body. In this paper, we discuss three categories of such devices: navigation systems, sensors and actuators for catheters and endoscopes, and other minimally invasive techniques. A brief introduction to principles, device structures, packaging, and related issues is presented.     

Characterizing the dependence of vegetation model parameters on crop structure, incidence angle, and polarization at L-band

To retrieve soil moisture over vegetation-covered areas from microwave radiometry, it is necessary to account for vegetation effects. At L-band, many retrieval approaches are based on a simple model that relies on two vegetation parameters: the optical depth (/spl tau/) and the single-scattering albedo (/spl omega/). When the retrievals are based on multiconfiguration measurements, it is necessary to take into account the dependence of /spl tau/ and /spl omega/ on the system configuration, in terms of incidence angle and polarization. In this paper, this dependence was investigated for several crop types (corn, soybean, wheat, grass, and alfalfa) based on L-band experimental datasets. The results should be useful for developing more accurate forward modeling and retrieval methods over mixed pixels including a variety of vegetation types.     

Closed loop control of excitation parameters for high speed switched-reluctance generators

This paper presents a new approach to the automatic control of excitation parameters for the switched-reluctance generator (SRG) where the SRG system operates at sufficiently high speed that it operates in the single pulse mode. The turn-on and turn-off angles are the two parameters through which we can control the electric power generation. The objective of the work is to develop an easily implementable control algorithm that automatically maintains the most efficient excitation angles in producing the required amount of electric power. The work is focused on finding the most efficient excitation angles and characterizing them for easy implemention under closed loop control. Through modeling of an experimental SRG and extensive simulation, it can be seen that the optimal-efficiency turn-off angles can be characterized as a function of power and speed level. Within the closed-loop power controller, the optimal-efficiency turn-off angle is determined from an analytic curve fit. The turn-on angle is then used as the degree of freedom necessary to regulate the power produced by the SRG. Given that the turn-off angle is associated with optimal-efficiency at each speed and power point, overall operation is achieved at optimal-efficiency. The SRG, inverter and control system are modeled in Simulink to demonstrate the operation of the system when implemented within a voltage regulation system. The control technique is then applied to an experimental SRG system. Experimental operation documents that the technique provides for efficient operation of the SRG system through tuning the controller at only four operating points.     

Hiding data in multitone images for data communications

Two novel data-hiding schemes for secure data communications are presented. These two schemes perform on the pixel differences between the original (host) image and the decompressed image, which is inspired from Wu's and Chao's methods. The first scheme, referred to as 'scheme-1', utilises the differences between two similar images and then embeds the secret data into the different parts. In the embedding process, two auxiliary techniques, zero-replacement and complement-bit, will also be incorporated. In addition, to enhance the hiding efficiency of scheme-1, the authors have followed the bit-plane hiding strategy and created scheme-2. The proposed schemes have two advantages. First, the error distortion can be measured before the hiding process begins. Second, there is no complex computation, which means the hiding process can be executed very efficiently. The experimental results show that the two proposed schemes can achieve better image quality than other data-hiding schemes. At the same time, the new schemes can also satisfy the three basic requirements a data hiding scheme should live up to: invisibility, capacity and data security.     

Integration of ultra-wideband slot antenna on LTCC substrate

An ultra-wideband slot antenna realised in low-temperature cofired ceramic (LTCC) technology is reported. The antenna is developed for a single-package solution of ultra-wideband radio. The radiating element of the antenna has a shape of ellipse 11 mm wide and 17 mm long. It shares the ground plane with other radio circuitry and is fed through a microstrip line 41 mm long and 3 mm wide. The experimental result shows that the prototype antenna achieved a bandwidth of 7.6 GHz (return loss S11/spl les/-10 dB or VSWR 2:1 from 3 to 10.6 GHz). The antenna radiation patterns at 3.5, 6.85 and 10.1 GHz are also presented.     

Validation of temporal BRDFs of paddy fields estimated from MODIS reflectance data

The effect of the bidirectional reflectance distribution function (BRDF) is one of the most important factors in correcting and validating the reflectance obtained from remotely sensed data. While the importance of BRDF has become widely recognized, bidirectional reflectance factor (BRF) data measured for correction and validation are insufficient because of the technical difficulty of the measurement. The primary objective of the present research is to estimate BRDF effects from Moderate Resolution Imaging Spectroradiometer (MODIS) data. Temporal ground-based BRDFs of rice paddy fields were estimated from ground measurements conducted in June and August 2002. MODIS-derived BRDFs obtained from MODIS reflectance data and ground-based BRDFs were estimated using the reciprocal form of the RossThick and LiSparse (RossThick-LiSparse-R) kernels, a semiempirical BRDF model adopted for the operational MODIS BRDF product. The MODIS-derived band 1 (620-680 nm) and band 2 (841-876 nm) BRDFs were compared with the ground-based BRDFs corresponding to the same waveband, respectively. The comparison results demonstrate that BRDFs of paddy fields change in accordance with paddy growth and that MODIS-derived BRDFs are closely related to ground-based BRDFs in most of the cases. It was also revealed that MODIS-derived BRDFs can be estimated to a high degree of accuracy when MODIS data necessary for the estimation are available.     

Effects of environmental uncertainty on organizational intention to adopt distributed work arrangements

Uncertainty in the external environmental context has been shown to affect organizational change and innovation. Distributed work arrangement is an organizational innovation that has the potential to enable a firm to meet the challenges of an uncertain environment more effectively. With the emergence of virtual organizations, such work arrangements are likely to gain increasing popularity. This exploratory empirical study employs a structural model to examine how environmental uncertainty affects organizational predisposition (adoption intention) toward distributed work arrangements. Environmental uncertainty has two different dimensions: environmental complexity (heterogeneity) and environmental variability (dynamism). In this paper, environmental dimensions are modeled to influence adoption of distributed work arrangements through shaping the organizational perceptions of three innovation characteristics: perceived relative advantage, compatibility and complexity. Data analyses using partial least squares statistical technique revealed that environmental complexity is negatively associated with perceived relative advantage, and perceived compatibility. Perceived relative advantage and perceived compatibility are in turn positively related to adoption intention for distributed work arrangements. However, environmental variability has no significant effect on the three innovation characteristics. Contrary to past findings that suggest organizations are more predisposed toward innovations in a complex environment, our study found that organizations in an environment of lower, rather than higher complexity are more likely to adopt distributed work arrangements. Implications for organizations are discussed.     

Watermarking scheme based on support vector machine for colour images

A novel watermarking scheme based on the support vector machine is proposed. The watermark is embedded in the blue channel of a colour image. By applying the embedded extra reference watermark, the support vector machine is trained, and then the watermark can be extracted by the trained support vector machine. Owing to the good generalisation ability of the support vector machine, even when the watermarked image is heavily distorted the watermark can be successfully extracted. Experimental results show good robustness of the proposed scheme.