A. Kashif

High performance GaN HEMT class-AB RF power amplifier for L-band applications

This paper presents the design and characterization of a GaN HEMT based class-AB power amplifier (PA) for L-band radar applications at 1.3 GHz. The aim of this paper is to design and develop a 30 Watt PA together with high efficiency, small in size and low-cost solution. The source and load impedances have been extracted by performing source and load-pull for attaining an optimal performance of class-AB PA. The fabricated PA provides an RF power of 45.5 dBm at 1-dB compression point. The power added efficiency (PAE) of 63% is achieved together with power gain of 13.5 dB at desired frequency.

Design and fabrication of a GaN HEMT based amplifier for wideband applications

This paper reports design, fabrication and measurements of a wideband amplifier for UHF applications. A technology based on Gallium Nitride (GaN) transistor is used to design a class- AB amplifier with compact dimensions which can be employed as a driver stage for many UHF applications with wideband requirements. Wideband impedance transformers at input and output of the amplifier are implemented to achieve the wideband features including higher gain and efficiency. The designed amplifier is fabricated and then characterized to verify the design parameters and it has been observed that the simulated results are in agreement with the measured ones. Maximum RF output of 5W (37dBm) is demonstrated over frequencies ranging from 150-500 MHz with gain flatness of 2.5dB. Flatness of ±0.5dB is shown within 220-500MHz. The measured power gain is found to be above 17dB for the entire band.

Switching behavior of RF-LDMOS for class-F power amplifier in TCAD

Nowadays the characterization of RF devices under large signal is performed in TCAD by using computational load-pull (CLP) simulation technique. In this paper, we modified the CLP simulation technique further to study the switching response of RF-LDMOS transistor for high efficiency switching power amplifier (e.g. class-F). In class-F PA operation, we achieved 85 % power added efficiency (PAE) together with 1.0 W/mm RF power density on the basis of finite harmonics. By this CLP technique, we can study the switching response of intrinsic RF-devices directly under large signal operation prior to fabrication or non-linear model of RF-transistor without including any external lumped matching networks.

High Power LDMOS Transistor for RF-Amplifiers

We designed simulated and optimized laterally diffused Si-MOSFET (LDMOS) transistors in Sentaurus TCAD software. By introducing excess interface charge density at the RESURF (reduced surface field) region, a power density 1.5 W/mm with a PAE (power added efficiency) of 45% at 3 GHz were obtained. The gain was 20.3 dB. These results show the enhancement in RF performance by introducing excess interface charge density at the RESURF region.

Two-stage GaN HEMT based class-C pulsed amplifier for S-band radar applications

High performance amplifiers are always demanding in wireless communication. To amplify RF signal, power amplifier is considered as a heart source of the system. We have designed and developed a high performance two-stage pulsed class-C broadband PA for moderate range surveillance radar applications in the frequency range from 2.45 - 2.75 GHz. A common source configuration is used to deliver peak RF output power above 38 dBm. Hence, this amplifier can be used as driver amplifier for high power surveillance radar applications etc. The measured RF peak power of the amplifier is ~ 39 dBm.

Design and implementation of bias sequence circuits for GaN HEMT amplifiers both pulsed and CW applications

GaN HEMT with silicon substrate is famous and considered as the next generation of RF power transistor technology. It has major advantages of high power, low cost and reliability etc., GaN HEMT requires special attention in bias circuit to avoid the instability of the device. Sequence circuit is required to supply voltages in order. In this paper, we have design and implemented the sequential circuits in bias network for pulsed and CW applications. MAX881R is used in power supply for pulsed while LTI1964ES5-BYP with R2D Recon 2405 is used for high current application in CW. For pulsed applications in ON sequence the gate is turned-on ~ 220 ms before the drain, while in OFF sequence the drain is turned-off ~ 1.7 s before the gate. While in CW applications in ON sequence the gate is turned-on ~ 130ms before the drain and in OFF sequence, the drain is turned-off ~ 633ms before the gate.

10 Watts UHF broadband GaN based power amplifier for multi-band applications

The demand of broadband amplifier has been boosted to meet the requirements of multi-mode and multi-band wireless applications. GaN HEMT is the next generation of RF power transistor technology. In this paper, we have designed a 10W UHF broadband class-AB Power Amplifier (PA) based on GaN HEMT. The proposed amplifier has been designed and developed in the frequency range from 200-500 MHz. A maximum drain efficiency of 71% is achieved.

Advantage of TCAD to analyze RF-LDMOS for the broadband power amplifier

Technology Computer Aided Design (TCAD) provides an alternate method to study the power amplifier (PA) design prior to fabrication and 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 the performance of a broadband PA based on computational load-pull (CLP) analysis. To validate TCAD approach, we have designed a broadband (1.9 - 2.5 GHz) class AB PA with an output matching network. The large signal simulation results verify the optimum impedance value (Zf) by providing a desired RF output power of 30.8 dBm.

Reduction in on-resistance of LDMOS transistor for improved RF performance

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.

A non-linear TCAD large signal model to enhance the linearity of transistor

In this paper, the proposed technique can be used to study the internal device non-linearity by TCAD device level simulations to enhance the device performance by physical structure/doping.A new large signal simulation technique to study non-linear effects of microwave power transistor