1 Watt linear amplifier for 13cm


A few weeks ago I wanted to built a small low-cost linear amplifier for some 13cm tests. I decided to use the RF2126 power amplifier IC form RFMD which is matched internally and requires only little matching networks (shunt + series capacitor) so I could mount it into a 40 x 50 mm brass box. This IC offers about 10 dB gain at 2.4 GHz and could be used for 23 cm, too, with slightly modified matching networks at the in- and output.

For driving the power module I use a Hittite MMIC with approximately 10 dB gain at a P1dB of ca. +22dBm which results in an input power of ~10 dBm to get +30dBm at the output.

The RF2126 is in a SO-8 housing with an "exposed pad" which serves as DC and RF ground and as heatsink, therefore I've cut a small stripe out of my PCB and replaced this by a 1.5 mm wide brass piece which is soldered to the brass housing with 180°C solder. The MMIC is soldered with 138°C SMD solder paste so you can put the whole amplifier onto a heating plate for easy IC replacement.

Here you can see the schematic of the amplifier, it is a very straight forward design using the part values of the application note in the datasheet.
The layout was chosen for best fit into the new housing; you should add some ground vias to avoid oscillation.
Here you can download the Eagle .sch and .brd file.


(c) Thomas Gulden, 03 / 2010