3.6V, 1W RF Power Transistors

for 900MHz Applications

4

_______________________________________________________________________________________

_______________Detailed Description

MAX2601/MAX2602

The MAX2601/MAX2602 are high-performance silicon

bipolar transistors in power-enhanced, 8-pin SO pack-

ages. The base and collector connections use two pins

each to reduce series inductance. The emitter connects

to three (MAX2602) or four (MAX2601) pins in addition

to a back-side heat slug, which solders directly to the

PC board ground to reduce emitter inductance and

improve thermal dissipation. The transistors are intend-

ed to be used in the common-emitter configuration for

maximum

power

gain

and

power-added

efficiency.

Current Mirror Bias

(MAX2602 only)

The MAX2602 includes a high-performance silicon

bipolar RF power transistor and a thermally matched

biasing diode that matches the power transistor’s ther-

mal and process characteristics. This diode is used to

create a bias network that accurately controls the

power transistor’s collector current as the temperature

changes (Figure 2).

The biasing diode is a scaled version of the power tran-

sistor’s base-emitter junction, in such a way that the

current through the biasing diode is 1/15 the quiescent

collector current of the RF power transistor. Supplying

the biasing diode with a constant current source and

connecting the diode’s anode to the RF power transis-

tor’s base ensures that the RF power transistor’s quies-

cent collector current remains constant through

temperature variations. Simply tying the biasing diode

to the supply through a resistor is adequate in most sit-

uations. If large supply variations are anticipated, con-

nect the biasing diode to a reference voltage through a

resistor, or use a stable current source. Connect the

biasing diode to the base of the RF power transistor

through a large RF impedance, such as an RF choke

(inductor), and decouple to ground through a surface-

mount chip capacitor larger than 1000pF.

5

Ω

T1

T2

L1

0.1

μF

2pF

L1 =

T1, T2 =

COILCRAFT A05T INDUCTOR, 18.5nH

1", 50

Ω TRANSMISSION LINE ON FR-4

1000pF

0.1

μF

1000pF

1000pF

1000pF

100nH

24

Ω

12pF

10pF

1

8

2, 6, 7

BACKSIDE

SLUG

4

5

2pF

Figure 1. Test Circuit

Q2

Q1

Figure 2. Bias Diode Application