Noise Figure Tuning Network

spflanze — Fri, 17 Nov 2017 03:58:18 GMT

In spec sheets such as this one:

https://community.nxp.com/external-link.jspa?url=https%3A%2F%2Fwww.nxp.com%2Fdocs%2Fen%2Fdata-sheet%2FBFT25A.pdf

there is are smith charts showing noise figure versus reflection coefficient data. In these smith charts does the reflection coefficient plotted in them show what it would without the transistor connected and the tuning network alone, or does it show what it is with the transistor connected?

In other words, to calculate what component values the tuning network had to have for any given reflection coefficient does the transistor base terminal's hybrid pi parameters have to be taken into account?

In that spec sheet's Tables 8 and 9 on page 7, and Table 10 on page 8 there is an Rn/50 column. What is Rn?

Re: Noise Figure Tuning Network

LPP — Tue, 28 Nov 2017 08:37:29 GMT

A noise circle is a locus of source impedances for a given noise figure as a function of frequency. Gamma values are provided as source reflection coefficient at 50 Ohm characteristic impedance. These are parameters of the signals source alone (without transistor connected).

>What is Rn?

Datasheet provides noise figure at the optimal source resistance. Rn is a fictitious equivalent noise resistance that is a measure of additional noise when the source resistance is not equal to the optimal value. Please, refer to the following documents:

https://ww2.minicircuits.com/app/AN60-040.pdf //equation #4
http://www.engineering-electronics.com/html/smith_chart_course.html //Matching example #13
http://www.ece.ucsb.edu/~long/ece145a/LNAdesign.pdf

Have a great day,
Pavel
NXP TIC

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