Chih Ming Tsai

New cross-coupled filter design using improved hairpin resonators

Stepped-impedance resonators have been thoroughly studied in this paper. Two equations for odd- and even-mode resonance are derived from a new network model. The size and resonant frequencies of the resonator could then be designed based on these two equations. A new resonator-embedded cross-coupled filter, constructed by stepped-impedance hairpin resonators and miniaturized hairpin resonators is presented. This new filter is very compact and has lower spurious response. A 0/spl deg/ feed structure, which adds two transmission zeros to the filter response, is also studied. The two zeros are so close to the passband that the selectivity and out-of-band rejection of the filter are significantly increased. The design has been verified by experiment results.

Performance of a planar filter using a 0/spl deg/ feed structure

The advantage of using a 0/spl deg/ feed structure in filter design is that two extra transmission zeros are created in the stopband while the passband response remains unchanged. This feed structure is analyzed by using transmission matrices. A new lumped-circuit model for a coupled resonator filter is then proposed to take into account the effects of this feed structure. Finally, the feed structure is applied to the design of a cross-coupled filter. All the theoretical analysis and design procedures have been successfully verified by experiment results.

Planar filter design with fully controllable second passband

New designs of the dual-band filter realized by distributed circuits are studied in this paper. Series and parallel open stubs are used as the resonators to fulfil the dual-band characteristics. Two dual-band inverters are proposed, which can be easily merged with adjacent resonators to reduce the circuit size. All the theoretical analysis and design procedures are discussed in detail and have been successfully verified by experiment results.

A generalized model for coupled lines and its applications to two-layer planar circuits

A generalized network model for asymmetrical and inhomogeneous coupled lines has been derived based on normal mode parameters. This model is useful for synthesis of single and multilayer coupled-line circuits, such as planar baluns and directional couplers. The synthesis procedures are described and have been verified by comparing with analysis results. >

High efficiency and improved ESD characteristics of GaN-based LEDs with naturally textured surface grown by MOCVD

The following paper presents a study on GaN-based light-emitting diodes (LEDs) with naturally textured surface grown by metal-organic chemical vapor deposition. The study utilizes a well-known approach of increasing light extraction efficiency. The approach is based on naturally formed V-shaped pits on surface that originate from low-temperature-growth (LTG) conditions of topmost p-GaN contact layer. In our experiment, the high-temperature-grown (HTG) p-GaN layer was inserted between the p-AlGaN electron-blocking layer and the LTG p-GaN contact layer, in order to suppress pit-related threading dislocations (TDs). These TDs may intersect the underlying active layer. The results of the experiment show that GaN-based LEDs with the HTG p-GaN insertion layer can effectively endure negative electrostatic discharge voltage of up to 7000 V. We also noted that application of 20-mA current injection yields output power of about 16 mW for the LEDs emitting around 465 nm. The output power results correspond to an external quantum efficiency of around 30%

Dual-band coupling and feed structure for microstrip filter design

A new configuration of dual-band filter design is presented in this paper. Stepped-impedance transmission-line sections are used as the tunable dual-band resonators. New coupling structures and matching networks at input and output are also proposed to achieve a dual-band characteristics. Three filters with their second passband at 1.5, 2, and 2.5 times the fundamental frequency are designed as examples, and they are all verified by experimental results.

Enhanced output power in GaN-based LEDs with naturally textured surface grown by MOCVD

GaN-based light-emitting diodes (LEDs) with naturally textured surfaces grown by MOCVD were demonstrated. In this study, a growth-interruption step and a surface treatment using biscyclopentadienyl magnesium (CP/sub 2/Mg) were simultaneously performed to form a plurality of nuclei sites on the surface of a p-type cladding layer, and then a p-type contact layer was grown on the p-type cladding layer, so as to create a p-type contact layer with a rough surface having truncated pyramids. Experimental results indicated that GaN-based LED with the truncated pyramids on the surface exhibited an enhancement in output power of 66% at 20 mA. It is worth noting that the typical 20-mA-driven forward voltage is only slightly higher than those of conventional LEDs (without the Mg-treatment process).

Dual-Band Filter Design With Flexible Passband Frequency and Bandwidth Selections

In this paper, improved dual-band filter design is studied. The dual-band resonators are composed of shunt open- and short-circuited stubs. In order to fulfil the requirements of dual-band inverters, a structure of stepped-impedance asymmetric coupled lines is proposed and its equivalent circuit is also derived. The dual-band filter is then designed based on this equivalent circuit. This type of filter can achieve relatively large practical passband center frequency ratios (in theory infinite), and it has more freedom of bandwidth ratio. The circuit size is also reduced. Detailed design procedure is presented and, finally, a filter example is given to validate the theoretical study

Transmission-line filters with capacitively loaded coupled lines

Coupled lines with loads at one end, which can create tunable transmission zeros, are studied in this paper. The equation for the transmission zeros is derived from the analysis of even- and odd-mode excitations. Based on this equation, coupled lines with different loads are analyzed and the rules for controlling the transmission-zero frequency are given. The structures are used in the designs of several second-order filters and they are experimentally verified. The use of a skew-symmetric (0/spl deg/) feed structure in these filters is also discussed and an example is given.

InGaN light-emitting diodes with naturally formed truncated micropyramids on top surface

GaN-based light-emitting diodes (LEDs) with truncated micropyramids surfaces performed by metalorganic chemical vapor deposition were demonstrated. In this study, a growth-interruption step and an Mg-treatment process were simultaneously performed to create multiple truncated micropyramids on LED surface. Experimental results indicated that GaN-based LEDs with the truncated micropyramids on the top surface demonstrate improved external efficiency of around 60% at 20mA. It is worth noting that the typical 20mA driven forward voltage is only 0.15V higher than that of conventional LEDs (LEDs with specular surface).