Farid Temcamani

Silicon carbide MESFETs performances and application in broadcast power amplifiers

We present DC, small signal and power characterization of recent Thomson silicon carbide MESFETs. We present also performances of SiC power amplifiers designed for use in broadcast digital television. A comparison with a LDMOS amplifier showed that SiC is a very promising material for microwave and RF power amplification.

Physical analysis of Schottky contact on power AlGaN/GaN HEMT after pulsed-RF life test.

This paper deals with the physical study of the Schottky contact after pulsed-RF saturated life test under enhanced drain bias voltage on power HEMTs. Electrical measurements showed a pinch-off voltage (VP) shift, a decrease of output power and average drain current while Photon Emission Microscopy (PEM) was used to identify the degradation distribution along the 80 fingers die. Finally, Transmission Electron Microscopy (TEM) is performed to point out the different Schottky degradation between a central finger and an outer one.

Trap-free process and thermal limitations on large-periphery SiC MESFET for RF and microwave power

In this paper, we present recent results on an SiC MESFET and we describe two of the main limitation mechanisms encountered: the self-heating and the trapping effects. Results on recent MESFET devices processed by THALES Research and Technology (TRT), Colombes, France, show that the trapping effects has been solved by using epitaxial layers on a higher purity 4H-SiC semi-insulating substrate sample made with a new technique by Okmetic, Vantaa, Finland. The association of two chips in the same case showed that the main limitation mechanism for power density originates from self-heating effects, which could be solved by optimizing the chip layout. 37.8-W output power at 500 MHz, 1.78-W/mm power density, and 35-dB third-order intermodulation-distortion ratio are the best obtained performances. An experimental analysis of trapping and self-heating effects on large-periphery SiC MESFETs is proposed in this paper.

Compared deep class-AB and class-B ageing on AlGaN/GaN HEMT in S-Band pulsed-RF operating life

AlGaN/GaN HEMTs are on the way to lead the RF-power amplification field according to their outstanding performances. However, due to its relative youth, reliability studies in several types of operating conditions allow to understand mechanisms peculiar to this technology and responsible for the wearing out of devices. This paper reports the reliability study on two power amplifiers using AlGaN/GaN HEMT. Based on results of a previous study of 1280 h in standard operating conditions wherein no evolution of electrical parameters have been observed, two ageing tests in deep class-AB (432 h) and class-B (795 h) are performed under pulsed-RF operating life at high drain bias voltages and saturated operation. This study shows a drift in RF performances which is linked with the evolution of electrical parameters (RDSON, gm and VP). Similar kinetics and amplitude of degradations are observed revealing quasi-similar contribution of thermal effects in both cases. Degradations are supposed to be related to trapped charges phenomena induced by high voltage operating conditions. Although, several results attest to this hypothesis, a part of the evolutions seems to be linked with structural changes.

CMOS RF active inductor with improved tuning capability

This paper presents an improved low power CMOS active inductor topology suitable for RF filtering. The circuit is derived from a previous designed transistor-only active inductor by adding a floating voltage source to one transistor gate fact that positively changes the overall dc biasing. If a current source with high output resistance is used for active inductor, this method can lead to lower interdependence between the self resonant frequency and quality factor. The simulations were carried out in 0.18µm CMOS technology.

Improved RF CMOS active inductor with high self resonant frequency

Many architectures of transistor only simulated inductors (TOSI) have been proposed until now in literature. Exhibiting tuning possibilities, low chip area and offering integration facility, they constitute promising architectures to replace passive inductors in RF circuits. An improved CMOS active inductor topology is proposed in this paper. With a novel loss compensation scheme, frequency increase up to 1.1 GHz (30%–66%) of the inductor self resonant frequency is achieved in the frequency band 1.5–3.3 GHz with large quality factors and very low current consumption. Besides, a more accurate passive model is proposed for CMOS TOSI active inductors and tested for this particular topology. Consisting of four parallel branches, it is still second order even though it contains three conservative elements. The model is sufficient general and proves superior performances over the classical RLC model mainly for higher frequencies. The simulations were carried out in a 0.18 um CMOS process.

Negative resistance based tuning of an RF bandpass filter

A novel tuning technique which improves the performances of an RF differential bandpass filter based on simulated inductors is presented. Gain enhancement techniques are applied to reduce the inductor losses by using an extra differential negative resistance. The proposed method is sufficiently general to be applied to other active filters topologies based on active inductors as well and is intended to be used for CMOS multi-standard filters design.

Frequency enhancement method applied to a CMOS RF simulated inductor BP filter

A new method for improving the frequency response of an all transistor simulated CMOS inductor bandpass filter is proposed. It is shown that a significant increase of the central frequency up to 800 MHz or even more can be obtained by introducing a supplementary resistor connected to the gate of one transistor. The method makes also use of negative resistances to compensate the inductor losses. Small signal models and limitations of the method are discussed. High quality factors are obtained without stability problems or extra power consumption. The simulations prove that the frequency enhancement depends on the particular configuration of the active inductor.

Microwave Active Filter using Finite Gain Amplifier

This paper deals with the design of microwave analog biquadratic filters using voltage amplifiers. A prototype bandpass filter is monolithically integrated. The chip size is only 1.3 mm2 on GaAs substrate. The filter specifications are: 2Ghz central frequency and a 3dB bandwidth of 40 MHz. A comparison with the SiGe bipolar technology is represented. The circuit represents a building block suitable for use in the cascade realization of higher order filters.

Bandwidth enhancement of an inverse class-F power amplifier based on LDMOS devices

In this article, we report the design of an inverse class-F power amplifier for L-band transmit/receive module based on LDMOS (laterally diffused metal oxide semiconductor) transistors. The objective was to obtain high power efficiency over a wide band. Measurements showed a minimum of 61% power added efficiency (PAE) and 10 W output power with a gain of 14 dB over a bandwidth of 200 MHz. Average measured performances are, respectively, 11.4 W (±1.4 W) output power and 62.8% (±1.8%) PAE; 64.5% maximum PAE associated with 12.7 W output power has been reached. These results are, to our knowledge, the highest reported combination of power efficiency and bandwidth.