Philips Semiconductors B.V.
Low cost DECT Power Amplifier
This note describes the application of two of the new 5th generation silicon bipolar RF transistors
in SOT343R plastic SMD package in a two-stage power amplifier (PA), designed for use in
DECT cordless telephone systems. These transistors, manufactured according to the new
double-poly process, are characterised by their high transition frequency (fT > 20 GHz) at low
supply voltages, resulting in a superior power gain at microwave frequencies, usually a field
dedicated to GaAs-devices. Two layers of polysilicon are used: one for contacting the base,
yielding a low base resistance and one to form the emitter, resulting in a steep emitter dope
profile and an effective emitter width of 0.5 µm. A buried N-layer (collector) is placed within a P-
substrate, which is connected to the emitter package lead, which enables the die to be placed
on the ground plane, reducing emitter inductance and thermal resistance. Figure 1 shows a
cross section of a double-poly buried layer transistor.
Figure 1: Cross section and package of the double-poly buried layer RF transistors.
With only two double-poly transistors a complete amplifier line-up can be realised, offering
26 dBm of output power with more than 26 dB power gain. The amplifier requires a single
supply voltage of 3.6 V and typically has 44% efficiency. The biasing circuitry uses only one
NPN transistor pair, which also performs load power adjustment and on/off switching functions.
Thanks to the low component count and simple matching networks the entire amplifier
(including bias part) only measures 10 x 20 mm.
As compared to a previous demonstration board, PH96060 (Preliminary Application Note
RNR-T45-96-T-838) this one offers lower additional component count, but is less suitable for
The main features of the PA are:
- low component count
- small size
- high efficiency
- single supply operation