2-658
RF5189
Rev A7 060127
Theory of Operation
The RF5189 is a two-stage device with a nominal gain of 25dB in the 2.4GHz to 2.5GHz ISM band. The RF5189 is
designed primarily for IEEE802.11B WLAN applications where the available supply voltage and current are limited. This
amplifier will operate to (and below) the lowest expected voltage made available by a typical PCMCIA slot in a laptop PC,
and will maintain required linearity at decreased supply voltages.
The RF5189 requires only a single positive supply of 3.0V nominal (or greater) to operate to full specifications. Power
control is provided through two bias control input pins (VREG1 and VREG2), but in most applications these are tied
together and used as a single control input.
There is no external matching required on the input and output of the part, thus allowing minimal bill of material (BOM)
parts count in end applications. Both the input and the output of the device are DC-blocked.
For best results, the PA circuit layout from the evaluation board should be copied as closely as possible, particularly the
ground layout and ground vias. Other configurations may also work, but the design process is much easier and quicker if
the layout is copied from the RF5189 evaluation board. Gerber files of our designs are available on request.
The RF5189 is not a difficult part to implement, but care in circuit layout and component selection is always advisable
when designing circuits to operate at 2.5GHz. The choke inductors on VCC2 and BIAS2GND should be chosen so that
they are parallel self-resonant at the frequency of operation. In addition, the supply side of the choke inductor on VCC2
should be bypassed with a capacitor that is series self-resonant at the frequency of operation.
In practice, VCC1 and the supply side of the choke on VCC2 will be tied to the same supply. It is important to isolate
VCC1 from other RF and low-frequency bypass capacitors on this supply line. This can be accomplished using a suit-
ably-long transmission line which is RF shorted on the other end as described above. Ideally the length of this line will be
a quarter wavelength, but it only needs to be long enough so that the effects of other supply bypass capacitors on the
VCC1 line are minimized. If board space is a concern, this isolation can also be accomplished with an RF choke inductor
or ferrite bead.
The RF5189 has primarily been characterized with a voltage on VREG1 and VREG2 of 2.7VDC. However, the RF5189
will operate from a wide range of control voltages. If you prefer to use a control voltage that is significantly different than
2.7VDC, contact RFMD Sales or Applications Engineering for additional data and guidance.
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