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MAX2602ESA

3.6V, 1W RF Power Transistors for 900MHz Applications

Maxim Integrated 

3.6V, 1W RF Power Transistors

for 900MHz Applications

__________Applications Information

Optimum Port Impedance

The source and load impedances presented to the

MAX2601/MAX2602 have a direct impact upon its gain,

output power, and linearity. Proper source- and load-

terminating impedances (ZS and ZL) presented to the

power transistor base and collector will ensure optimum

performance.

For a power transistor, simply applying the conjugate of

the transistor’s input and output impedances calculated

from small-signal S-parameters will yield less than opti-

mum device performance.

For maximum efficiency at VBB = 0.75V and VCC =

3.6V, the optimum power-transistor source and load

impedances (as defined in Figure 3) are:

At 836MHz: ZS = 5.5 + j2.0

ZL = 6.5 + j1.5

At 433MHz: ZS = 9.5 - j2.5

ZL = 8.5 - j1.5

ZS and ZL reflect the impedances that should be pre-

sented to the transistor’s base and collector. The pack-

age parasitics are dominated by inductance (as shown

in Figure 3), and need to be accounted for when calcu-

lating ZS and ZL.

The internal bond and package inductances shown

in Figure 3 should be included as part of the end-

application matching network, depending upon exact

layout topology.

Slug Layout Techniques

The most important connection to make to the

MAX2601/MAX2602 is the back side. It should connect

directly to the PC board ground plane if it is on the top

side, or through numerous plated through-holes if the

ground plane is buried. For maximum gain, this con-

nection should have very little self-inductance. Since it

is also the thermal path for heat dissipation, it must

have low thermal impedance, and the ground plane

should be large.

4

2.8nH

3

2

MAX2601

MAX2602

1

2.8nH

2.8nH

ZS

5

6

2.8nH

ZL

7

8

Figure 3. Optimum Port Impedance

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