Analysis of temperature and process variation effects on photo sensor circuits using device/circuit mixed-mode simulations
Impact of temperature and process variations on the output voltage variations of CMOS photo sensor is discussed. As temperature becomes high, output voltage (Vout) decreases because of the amplifier characteristics. But above 350 K, Vout increases in a weak light intensity range. The process variations have an impact when the operation temperature is high and irradiating light intensity is low. We also estimate influence of additional drive-in process, and find the sensitivities of process variation to increase. To consider both process and temperature variations at the same time, we evaluate Vout variation with mixed-mode simulation.
Physics-Based Photodiode Model Enabling Consistent Opto-Electronic Circuit Simulation
The paper developed a photodiode (PD) model for circuit simulation considering, contrary to existing models, the transient carrier generation explicitly in the solution of the continuity equation. The developed model is compatible with conventional compact electrical device models and is demonstrated to enable accurate simulation of opto-electronic integrated circuits. The electric field distribution along the depth direction of the PD is found to cause a tail in the photo current, which has an adverse effect on optical response of PD and the performance of opto-electronic circuits. The developed opto-electronic circuit model is also applicable to predict how circuit performance is improved with respect to the improvement of photo diode characteristics
Neutron Residual Stress Measurements on Rail Sections for Different Production Conditions
Rail sectioning with subsequent neutron diffraction experiments has been used to assess residual stresses in the rails. In this study we present the results of neutron stress measurements performed at the NIST Center for Neutron Research (NCNR) on rail sections from rails that were produced under various conditions. Specifically, these are air-cooled, air-cooled and roller-straightened, head-hardened and head-hardened and roller-straightened. More significantly, a head-hardened and roller-straightened rail was also studied after service to elucidate evolution of the service-induced residual stresses. In the latter case both a transverse-cut slice and the central region of a 0.53 m long piece were studied. Measurements on this piece are the first in which triaxial stresses have been determined for an intact rail. Neutron strain measurements with 3×3×3 mm3 spatial resolution were successfully employed for transversally cut slices to verify the difference in the stress state depending on the production process. Although examination of slices allows determination of only two-dimensional stresses in the plane of the slice, additional measurements on obliquely-cut slices, which were also carried out, and utilization of FEM gives the possibility of reconstructing the full triaxial stress distribution. Together, these approaches provide a better understanding of rail fabrication and the possibility of improving the durability and safety of rails in the future.Copyright © 2004 by ASME