| 1. |
- Herzig, Sebastian, et al.
(författare)
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A CONCEPTUAL FRAMEWORK FOR CONSISTENCY MANAGEMENT IN MODEL-BASED SYSTEMS ENGINEERING
- 2011
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Ingår i: Proceedings of the ASME 2011 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference IDETC/CIE 2011. - : ASME. - 9780791854792 ; , s. 1329-1339
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Konferensbidrag (refereegranskat)abstract
- Developing complex engineering systems requires theconsolidation of models from a variety of domains such aseconomics, mechanics and software engineering. These modelsare typically created using differing formalisms and bystakeholders that have varying views on the same problemstatement. The challenging question is: what is needed to makesure that all of these different models remain consistent duringthe design process? A review of the related literature revealsthat this is still an open challenge and has not yet beeninvestigated at a fundamental level within the context ofModel-Based Systems Engineering (MBSE). Therefore, thispaper specifically focuses on examining the fundamentals ofconsistency management. We show that some inconsistenciescannot be detected and come to the conclusion that it isimpossible to say whether or not a system is fully consistent. Inthis paper, we first introduce a mathematical foundation todefine consistency in a formal manner. A decision-basedapproach to design is then studied and applied to thedevelopment of a real-world example. The research revealsseveral distinct types of inconsistencies that can occur duringthe design and development of a system. We show that theseinconsistencies can be further classified into two groups:internal and external consistency. From these insights, theontology of inconsistencies is constructed. Finally,requirements for possible tool support and methods to identifyand manage specific types of consistency issues are proposed.
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| 2. |
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| 3. |
- Kashif, Ahsan-Ullah, et al.
(författare)
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A TCAD approach for non-linear evaluation of microwave power transistor and its experimental verification by LDMOS
- 2010
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Ingår i: Journal of Computational Electronics. - : SpringerLink. - 1569-8025 .- 1572-8137. ; 9:2, s. 79-86
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Tidskriftsartikel (refereegranskat)abstract
- A simulation technique is developed in TCAD to study the non-linear behavior of RF power transistor. The technique is based on semiconductor transport equations to swot up the overall non-linearity’s occurring in RF power transistor. Computational load-pull simulation technique (CLP) developed in our group, is further extended to study the non-linear effects inside the transistor structure by conventional two-tone RF signals, and initial simulations were done in time domain. The technique is helpful to detect, understand the phenomena and its mechanism which can be resolved and improve the transistor performance. By this technique, the third order intermodulation distortion (IMD3) was observed at different power levels. The technique was successfully implemented on a laterally-diffused field effect transistor (LDMOS). The value of IMD3 obtained is −22 dBc at 1-dB compression point (P 1 dB) while at 10 dB back off the value increases to −36 dBc. Simulation results were experimentally verified by fabricating a power amplifier with the similar LDMOS transistor.
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| 4. |
- Kashif, Ahsan-Ullah, et al.
(författare)
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A TCAD Approach to Design a Broadband Power Amplifier
- 2010
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Technology Computer Aided Design (TCAD) provides an alternate method to study the power amplifier (PA) design prior to fabrication. It is very useful for the extraction of an accurate large signal model. This paper presents a design approach from device to circuit level to study broadband PA performance of RF-LDMOS using computational load-pull (CLP) analysis. To validate the TCAD approach, we have designed a broadband (1.9 - 2.5 GHz) class AB power amplifier. The concept is verified by designing an output broadband matching network at optimum impedance value (Zf) of RF-LDMOS using ADS software. The large signal results verify this concept and RF output power of 30.8 dBm is achieved with comparable gain and efficiency.
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| 5. |
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| 6. |
- Kashif, Ahsan-Ullah, 1974-, et al.
(författare)
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Flexible power amplifier designing form device to circuit level by computational load-pull simulation technique
- 2008
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Ingår i: Microelectonics Technology and Devices - SBMicro 2008, Vol. 14, issue 1. - Pennington, New Jersey : Electrochemical Society. - 9781566776462 ; , s. 233-239
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Konferensbidrag (refereegranskat)abstract
- Matchingnetwork is major issue in broadband power amplifiers due tothe fact that the transistor impedances are varying both withfrequency and signal level. Thus it is difficult to matchthese impedances both at the input and output stages. Thetunable matching networks are very demanding and desired for buildingflexible systems, but their accuracy depends on the transistor performanceunder the large signal operation. Computational load pull (CLP) simulationtechnique is a unique way to extract the impedances ofpower transistor at desired frequencies which make the design ofmatching network much easier for multiple bands power amplifiers. AnLDMOS transistor is studied and its optimum impedances are extractedat 1, 2 and 2.5 GHz. Through optimum impedance, thetunable matching networks can be easily design for broadband amplifiers.
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| 8. |
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| 9. |
- Kashif, Ahsan-Ullah, et al.
(författare)
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Influence of interface state charges on RF performance of LDMOS transistor
- 2008
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Ingår i: Solid-State Electronics. - : Elsevier. - 0038-1101 .- 1879-2405. ; 52:7, s. 1099-1105
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Tidskriftsartikel (refereegranskat)abstract
- Si-LDMOS transistor is studied by TCAD simulation for improved RF performance. In LDMOS structure, a low-doped reduced surface field (RESURF) region is used to obtain high breakdown voltage, but it reduces the transistor RF performance due to high on-resistance. The interface charges between oxide and the RESURF region are studied and found to have a strong impact on the transistor performance both in DC and RF. The presence of excess interface state charges at the RESURF region results not only higher DC drain current but also improved RF performance in terms of power, gain and efficiency. The most important achievement is the enhancement of operating frequency and RF output power is obtained well above 1 W/mm up to 4 GHz.
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| 10. |
- Kashif, Ahsan-Ullah
(författare)
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Optimization of LDMOS Transistor in Power Amplifiers for Communication Systems
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The emergence of new communication standards has put a key challenge for semiconductor industry to develop RF devices that can handle high power and high data rates simultaneously. The RF devices play a key role in the design of power amplifiers (PAs), which is considered as a heart of base-station. From economical point of view, a single wideband RF power module is more desirable rather than multiple narrowband PAs especially for multi-band and multi-mode operation. Therefore, device modeling has now become much more crucial for such applications. In order to reduce the device design cycle time, the researchers also heavily rely on computer aided design (CAD) tools. With improvement in CAD technology the model extraction has become more accurate and device physical structure optimization can be carried out with less number of iterations.LDMOS devices have been dominating in the communication field since last decade and are still widely used for PA design and development. This thesis deals with the optimization of RFLDMOS transistor and its evaluation in different PA classes, such as linear, switching, wideband and multi-band applications. For accurate evaluation of RF-LDMOS transistor parameters, some techniques are also developed in technology CAD (TCAD) using large signal time domain computational load-pull (CLP) methods.Initially the RF-LDMOS is studied in TCAD for the improved RF performance. The physical intrinsic structure of RF-LDMOS is provided by Infenion Technologies AG. A reduced surface field (RESURF) of low-doped drain (LDD) region is considered in detail because it plays an important role in RF-LDMOS devices to obtain high breakdown voltage (BVDS). But on the other hand, it also reduces the RF performance due to high on-resistance (Ron). The excess interface state charges at the RESURF region are introduced to reduce the Ron, which not only increases the dc drain current, but also improve the RF performance in terms of power, gain and efficiency. The important achievement is the enhancement in operating frequency up to 4 GHz. In LDD region, the effect of excess interface charges at the RESURF is also compared with dual implanted-layer of p-type and n-type. The comparison revealed that the former provides 43 % reduction in Ron with BVDS of 70 V, while the later provides 26 % reduction in Ron together with BVDS of 64 - 68 V.In the second part of my research work, computational load pull (CLP) simulation technique is used in TCAD to extract the impedances of RF-LDMOS at different frequencies under large signal operation. Flexible matching is an issue in the design of broadband or multi-band PAs. Optimum impedance of RF-LDMOS is extracted at operating frequencies of 1, 2 and 2.5 GHz in class AB PA. After this, CLP simulation technique is further developed in TCAD to study the non-linear behavior of RF devices. Through modified CLP technique, non-linear effects inside the transistor structure are studied by conventional two-tone RF signals in time domain. This is helpful to detect and understand the phenomena, which can be resolved to improve the device performance. The third order inter-modulation distortion (IMD3) of RF- LDMOS was observed at different power levels. The IMD3 of −22 dBc is obtained at 1-dB compression point (P1-dB), while at 10 dB back off the value increases to −36 dBc. These results were also verified experimentally by fabricating a linear PA. Similarly, CLP technique is developed further for the analysis of RF devices in high efficiency operation by investigating the odd harmonic effects for the design of class-F PA. RF-LDMOS can provide a power added efficiency (PAE) of 81.2 % in class-F PA at 1 GHz in TCAD simulations. The results are verified by design and fabrication of class-F PA using large signal model of the similar device in ADS. In fabrication, a PAE of 76 % is achieved.
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