Millimeter-wave AlGaAs-GaAs HBT power operation
The AlGaAs-GaAs HBT has demonstrated good power performance up to 18 GHz. Although f/sub max/ is typically above 100 GHz, the power performance limitation and large signal operation at millimeter wave frequencies have not been studied. Power results from two HBT structures at 35 GHz are analyzed based on numerical simulation. The HBT demonstrated 8.5-dB linear power gain, 30% PAE with 7.8-dB gain and 7.5-V V/sub ce/ bias. The power density reaches 1.25 mW/ mu m/sup 2/. A shorter collector (0.4 mu m) is shown to be better suited for 35-GHz operation as a result of shorter collector transit time and smaller residual collector voltage. Improvement can be achieved by reducing the base and collector resistance, and the collector capacitance.<<ETX>>
18 GHz high gain, high efficiency power operation of AlGaAs/GaAs HBT
Outstanding power performance has been achieved from an AlGaAs/GaAs heterostructure bipolar transistor (HBT) at 18 GHz. A common emitter HBT has achieved 48.5% added efficiency, 6.2-dB associated gain, and 0.17-W output power. Common base operation of the HBT exhibits higher gain at 18 GHz: 0.358 W (3.58 W/mm) was achieved with 11.4-dB gain and 43% added efficiency; at a reduced power level of 0.174 W (1.74 W/mm), 15.3-dB associated power gain was achieved with 40% efficiency. This performance compares favorably with the results reported for MESFETs, HEMTs (high-electron-mobility transistors), and PBTs (permeable-base transistors).<<ETX>>
Investigation of scatter radiation of non-circular X-ray scan trajectories
Modern interventional X-ray devices are highly maneuverable and allow complex 3D imaging trajectories. New scan trajectories enable not only optimized object sampling but also introduce new approaches for dynamic 3D imaging. In this paper, we investigated the scatter radiation of two different scan trajectories. The scatter radiation was sampled by a rail setup with dosimeters at defined positions. After data analysis, contour maps were generated which show for four exemplary heights the scatter radiation distribution. The alternative scan trajectory showed smaller dose exposures at heights correlated to upper torso and head areas of a model physician. Keywords—Image acquisition, alternative scan trajectory, circular tomosynthesis, scatter radiation distribution