Illustration par trois exemples: doubleur de frequence a transistor a effet de champ, conception d'un amplificateur de puissance avec reduction de la distorsion d'intermodulation, amplificateur limiteur

Nonlinear circuit design using the modified harmonic balance algorithm

This paper presents an analytical study of the RF performance of Si power MOSFET's. Si MOSFET's are rapidly becoming popular in RF applications. Although circuit simulation models have been presented explaining the static performance of these devices, the correlation of device physical parameters with RF performance has not been studied extensively. In this paper, based on the equivalent circuit representation of a power MOSFET, static and large-signal analysis have been carried out to study the RF performance for VDMOSFET and LDMOSFET devices. It has been shown that transconductance compression due to the JFET region leads to degradation of high-power RF performance. It is also shown that LDMOSFET has higher power gain than VDMOS, but steeper degradation with input power. Velocity saturation in the MOS channel and presence of the JFET region are shown to strongly influence the RF performance of the two devices.

Performance modeling of RF power MOSFETs

This paper describes a dedicated nonlinear MESFET model, which was used to accurately represent the device's drain-source current nonlinearity. An analytical expression is proposed, based on the Shockley approach, with good derivative reproduction. The evolution of the Ids(Vgs, Vds) Taylor-series-expansion coefficients across V/sub GS/ and V/sub DS/ revealed not only the presence of important minimum conversion loss bias, but also of in-band intermodulation distortion sweet spots that have been used to optimize an FET resistive mixer performance. Some previously reported experimental results are also discussed through the use of the derivatives, and an alternative topology is considered for resistive mixers working on the border between the linear and saturated regions.

Resistive FET mixer conversion loss and IMD optimization by selective drain bias

This paper discusses, in a mathematical form and supported by a complete special experimental characterization, the gate-to-source nonlinear capacitor contribution on small-signal intermodulation distortion (IMD) as well as other nonlinear related phenomena such as the onset of phase distortion and gain compression in GaAs FET devices. A simplified one-sided version of our previously proposed test setup and its corresponding characterization formulation are shown to conform a direct technique to extract the second- and third-order coefficients for the Cgs(Vgs) Taylor-series expansion. The extracted terms let us evaluate some of the most widely employed equations for this reactive nonlinearity according to their capability of reproducing its small-signal nonlinear distortion contribution. They are also shown to be responsible for some previously detected differences on IMD behavior at high frequencies and for significant variations on the load selection criteria for high carrier-to-intermodulation ratio and high output-power tradeoffs.

Characterizing the gate-to-source nonlinear capacitor role on GaAs FET IMD performance

We propose a new symmetrical heterojunction FET (HFET)/MESFET model to predict intermodulation distortion in amplifiers and resistive mixers. The model is symmetric. That is, drain and source of the intrinsic FET are interchangeable. This reflects the characteristics of most microwave FET's. The model has few fitting parameters and they are simple and straightforward to extract. The model was installed into Hewlett-Packard's harmonic-balance program microwave design system and verified by measurements. The verification shows excellent results for an MESFET and an HFET in both amplifier and resistive mixer configurations.

A symmetrical nonlinear HFET/MESFET model suitable for intermodulation analysis of amplifiers and resistive mixers

An accurate, detailed analysis program has been developed for intermodulation distortion (IMD) simulation of FET mixers. This program is very efficient at calculating the IMD from multiple RF inputs. We have proposed a simplified nonlinear model for IMD analysis of FET gate mixers. The accuracy of the simplified model has been verified experimentally using two different MESFET mixers and one HEMT mixer at X band. All the tests show good agreement between measured results and the calculated results for second- and third-order IMD. The simplified model is based on modeling the derivative of the device transconductance by a sum of a Gaussian function and a linear function of the gate voltage. Drain bias dependence is ignored. The advantage of this model is that it can be used for both MESFET and HEMT mixers, and its fitting parameters can be easily determined from a nonlinear characterization of the devices at low frequencies. >

Nonlinear models for the intermodulation analysis of FET mixers

We have implemented the Volterra-series method to analyze intermodulation (IM) distortion in FET resistive mixers. The nonlinearities of the channel conductance of a NE71000 MESFET and a NE32400 HFET were first characterized using a low-frequency harmonic power measurement. The data was then used in a simulation program and results for two-tone IM distortion in X-band were compared with the measured data for both MESFET and HFET resistive mixer circuits. Very good agreement was achieved in each case. We have also shown by simulation that the two separate contributions to the third-order IM distortion from the mixing between the input signals themselves and the mixing between the input signals and the second-order mixing products have a very strong cancellation, which results in the low IM distortion in the FET resistive mixers observed in measurements.

S. Peng

Papers

Nonlinear models for the intermodulation analysis of FET mixers

Intermodulation analysis of FET resistive mixers using Volterra series