Philips Semiconductors B.V.

Low cost DECT Power Amplifier

PH97005

RNR-T45-97-M-0931

INTRODU CTION

This note describes the application of two of the new

5

in SOT343R plastic SMD package in a two-stage power amplifier (PA), designed for use in

DEC T cordless telephone systems. These transistors, manufactured according to the new

double-poly process, are characterised by their high transition frequency (f

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 t ransistors.

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 netw orks 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

PHS application.

The main features of the PA are:

- low component count

- small size

- high efficiency

- single supply operation

1 base

2 emitter

3 col lector

4 emitter