一种采用双环和自适应开关频率控制的恒压-恒流控制芯片的设计

本文设计了一款输出5V/2.0A的恒压(CV)-恒流(CC)控制芯片,采用flyback架构和源边反馈.该芯片采用双反馈环精确控制输出电压和输出电流,使得系统在工艺与温度等参数变化时具有更好的调整性能,优于通常使用的开环控制方法。同时系统可以根据输出电压值在恒压和恒流模式之间实现自动和平滑的切换,因而不会影响切换过程中的电压和电流调制精度,这很好地克服了使用迟滞比较器实现模式切换的数字控制方式的不足。通过采用有源电容倍增技术对电压反馈环实现片上补偿,可以不增加额外的封装管脚,并且有效地节省了芯片面积.为了在不牺牲瞬态响应性能的前提下减小芯片的无负载功耗,芯片应用了自适应开关频率控制模式,在轻载模式下,可自动降低开关频率以减小功耗.最低功耗可小于100mW .采用0.35-μm 40-V BCD工艺完成流片,芯片面积为1.5mm 1.0mm.由于线性调整度和负载调整度所造成的输出电压误差小于 1.7%.     

γ radiation caused graphene defects and increased carrier density

We report on a micro-Raman investigation of inducing defects in mono-layer, bi-layer and tri-layer graphene by γ ray radiation. It is found that the radiation exposure results in two-dimensional (2D) and G band position evolution with the layer number increasing and D and D' bands rising, suggesting the presence of defects and related crystal lattice deformation in graphene. Bi-layer graphene is more stable than mono- and tri-layer graphene, indicating that the former is a better candidate in the application of radiation environments. Also, the DC electrical property of the mono-layer graphene device shows that the defects increase the carrier density.     

Analytical model for the dispersion of sub-threshold current in organic thin-film transistors

This paper proposes an equivalent circuit model to analyze the reason for the dispersion of sub-threshold current(also known as zero-current point dispersion) in organic thin-film transistors.Based on the level 61 amorphous silicon thin-film transistor model in star-HSPICE,the results from our equivalent circuit model simulation reveal that zero-current point dispersion can be attributed to two factors:large contact resistance and small gate resistance.Furthermore,it is found that decreasing the contact resistance and increasing the gate resistance can efficiently reduce the dispersion.If the contact resistance can be controlled to 0Ω,all the zero-current points can gather together at the base point.A large gate resistance is good for constraining the dispersion of the zero-current points and gate leakage.The variances of the zero-current points are 0.0057 and nearly 0 when the gate resistances are 17 MΩand 276 MΩ,respectively.     

有机薄膜晶体管中亚阈值电流分散的模型分析

本文提出了一个等效电路模型以分析在有机薄膜晶体管中引起亚阈值电流漂移(也叫零电流点漂移)现象的原因. 该等效电路模型基于Start-HSPICE中的Level 61无定形硅薄膜晶体管器件模型. 仿真结果表明零电流点漂移的原因可以归结于两点: 接触电阻和栅电阻. 更进一步发现, 减小接触电阻和增大栅电阻可以有效抑制零电流点漂移现象. 如果接触电阻可以减到0, 则所有的零电流点交于原点, 此时没有漂移. 增大栅电阻对于抑制零电流点漂移和栅漏电也是有好处的. 当栅电阻分别为17 MΩ和276 MΩ时, 零电流点坐标值的方差分别为0.0057和接近于0.