Philips Semiconductors B.V.

Low cost DECT Power Amplifier

PH97005

RNR-T45-97-M-0931

Impedance matching

The impedance matching part consists of three separate sections: the input, the interstage and

the output matching networks. The purpose of these networks is to enable the RF transistors to

give optimum performance w ith respect to power gain, output power and efficiency. Fortunately,

the impedance levels of the applied

double-poly transistors are not exceptionally high or low, so

they’re rather easy to match.

Decoupling is done by using capacitors C1, C4, C6, C8, C 11 and C12, which are series

resonant at 1.9 GHz. C apacitors C7 (with resistor R3) and C 9 are used to suppress low

frequency instability.

At the input side shunt capacitor C2 and series

transmission line TL1 match the 50

Ω source to the

base of Q1. Base resistor R1 is used for biasing and

has no effect on matching.

Fig. 3a: Input mat ching.

Between the collector of Q1 and the base of Q2

matching is done by series transmission line TL2, shunt

capacitor C3 and series transmission lines TL4 and

TL6. Both shunt capacitors C3 and C5 (partly)

compensate the influence of bias stubs TL3 and TL5,

which are both shorter than a quarter wavelength.

Fig. 3b: Interstage m at ching.

The output match is done by series transmission line

TL7 and shunt capacitor C10. Again this capacitor also

compensates the influence of bias stub TL6.

Fig. 3c: Output matching.

input Q1

C2

TL1

output Q1

input Q2

TL2

TL3

C3

TL4/TL6

TL5/C5

TL7

C10

output Q2