Philips Semiconductors B.V.

Low cost DECT Power Amplifier

PH97005

RNR-T45-97-M-0931

CIRCUIT DESCRIPTION

Figure 2 shows circuit diagram of the DECT PA including both RF transistors, matching circuits

and biasing circuit. The appendix contains the part list of the demo board.

Figure 2:Circuit

diagram of t he DECT PA demo board PH97005.

RF transistors

The RF chain of the PA consists of two transistor stages: a BFG425W (Q1) wideband transistor,

operating in class A and aBFG21W (Q2), operating in class AB.

In accordance with the above settings the measured source and load impedances of both

transistors are given in table 2.

Transistor

Source impedance (Z

Load impedance (Z

BFG425W

(V

12 + 0.7 j

Ω

52 + 102 j

Ω

BFG21W

(V

8 - 4.5 j

Ω

12 - 3.5 j

Ω

Table 2 : Source and load impedances of the applied RF transist ors.

Small signal S-parameter data for the BFG425W as well as large signal Spice parameters of

both the BFG425W and the BFG21W are available on floppy disc.

The RF transistors have tw o emitters leads, which have to be carefully grounded to ensure

stable operation and performance according to specification. Typically, the inductance of the

vias has to be kept below 0.1 nH.

Vs

Vc

RF in

RF out

C1

C4

TL1

Q1

R1

Q2

R5

TL2

C7

C2

TL3

TL4

C3

C5

TL5

TL6

TL7

TL8

C6

C8

C9

C10

C11

C12

C13

R2

R3

R4

R5

R6

R7

Q3a

Q3b