Thu, 24 Jul 2008 23:19:29 BST CiteULike: dcastros Hickson http://www.citeulike.org/user/dcastro/author/Hickson CiteULike.org en-gb Copyright © 2004-2008 citeulike.org http://www.citeulike.org/user/dcastro/article/2782066 <i>Microwave Symposium Digest, 1992., IEEE MTT-S International (1992), pp. 277-280 vol.1.</i><br /><br />Four models have been developed and assessed for fitting the measured noise parameters up to 26 GHz and S-parameters up to 400 GHz for a commercial HEMT (high electron mobility transistor) chip. The first treats the intrinsic noise sources as uncorrelated thermal sources. The second is an extension of this, allowing a better fit to be achieved by including the distributed nature of the gate and drain electrodes using a semidistributed, sliced model. The third model neglects the distributed effect but takes into account the partial correlation of the gate and drain noise sources. This causes a larger improvement in the quality of fit, allowing the model to fit the measured data within reasonable measurement limits. The addition of the distributed effect to the correlated model gives the fourth model, which allows a further marginal improvement, but the conditioning of the problem and the accuracy of the data appear to be insufficient to allow accurate extraction of the additional parameters needed HEMT models for S-parameter and noise parameter extrapolation MT Hickson P Gardner DK Paul doi:10.1109/MWSYM.1992.187966 Microwave Symposium Digest, 1992., IEEE MTT-S International (1992), pp. 277-280 vol.1. 2008-05-10T00:03:25-00:00 1992 Microwave Symposium Digest, 1992., IEEE MTT-S International 277 280 vol.1 model noise parameter http://www.citeulike.org/user/dcastro/article/2776111 <i>Electronics Letters, Vol. 29, No. 16. (1993), pp. 1408-1409.</i><br /><br />The limited gain available from GaAs FETs and HEMTs at millimetric frequencies can be overcome by using the devices in a negative resistance amplifier configuration. The advantage of the solid-state negative resistance amplifier over the transmission amplifier is that the gain available is not limited by the active device used. It has been shown that, over a narrow bandwidth, significantly higher gain can be obtained from a negative resistance amplifier, when compared to a transmission amplifier using the same device, while maintaining the same overall noise performance. This has been demonstrated experimentally using a 0.25 μm HEMT device High gain millimetric negative resistance low noise amplifiers MT Hickson P Gardner DK Paul Electronics Letters, Vol. 29, No. 16. (1993), pp. 1408-1409. 2008-05-09T15:18:07-00:00 1993 Electronics Letters 29 16 1408 1409 amplifier gain high low noise http://www.citeulike.org/user/dcastro/article/2776103 <i>Microwave Theory and Techniques, IEEE Transactions on, Vol. 40, No. 8. (1992), pp. 1709-1712.</i><br /><br />A model is described for a low noise millimeter-wave HEMT device. It takes account of the distributed nature of the gate and drain electrodes by dividing the active region of the device into a number of slices. Each slice is modeled as an intrinsic HEMT with thermal noise sources and the slices are connected together through lossy reactances. The parameters of the first slice are made different from those of the remaining slices, in order to account for the inevitable differences in the field distribution in the gate feed region. The model parameters have been optimized numerically to fit the manufacturer's measured S-parameters and all four noise parameters, for a commercially available HEMT chip. A good fit has been achieved simultaneously to all of these parameters, and the model therefore provides a reasonable basis for extrapolation to higher frequencies. The significance of the distributed gate effect and the unequal slice effect is assessed by comparing the best fit achievable when these effects are not included A semidistributed HEMT model for accurate fitting and extrapolation of S-parameters and noise parameters MT Hickson P Gardner DK Paul doi:10.1109/22.149534 Microwave Theory and Techniques, IEEE Transactions on, Vol. 40, No. 8. (1992), pp. 1709-1712. 2008-05-09T15:16:17-00:00 1992 Microwave Theory and Techniques, IEEE Transactions on 40 8 1709 1712 fet model noise