2-243
RF2163
Rev A6 060301
Theory of Operation and Application Information
The RF2163 is a two-stage device with a nominal gain of 19dB in the 2.4GHz to 2.5GHz ISM band. The RF2163 is
designed primarily for IEEE802.11B WLAN applications where the available supply voltage and current are not limited. It
will meet 802.11B spectral mask requirements at an output power of +24dBm. It is especially appropriate for WLAN
access points and other base-station type equipment.
The RF2163 requires only a single positive supply of 3.3V 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 some external matching on the input and output of the part, thus allowing the part to be used in other applica-
tions outside the 2.4GHz to 2.5GHz ISM band (such as MMDS). Both the input and the output of the device need a
series DC-blocking capacitor. In some cases, a capacitor used as a matching component can also serve as the blocking
cap. The circuit used on the evaluation board is optimized for 3.5V nominal applications.
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 RF2163 evaluation board. Gerber files of our designs can be provided upon request.
The RF2163 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 most critical passive components in the circuit are the input, inter-
stage and output matching components (C1, C5, C6, C7, and C11). In these cases, high-Q capacitors suitable for RF
applications are used on our evaluation board (a BOM is available on request). High-Q parts are not required in every
design, but it is very strongly recommended that the original design be implemented with the same or similar parts used
on our evaluation board. Then, less costly components can be substituted in their place, making it easy to test the impact
of cheaper components on performance. General RFMD experience has indicated that the slightly higher cost of better
quality passive components is more than offset by the significant improvements in production yields in large-volume
manufacturing.
The interstage matching capacitor, C11, along with the combined inductance of the internal bond wire, the short length
of circuit board trace, and the parasitic inductance of this capacitor, tunes the peak of the small-signal gain response.
The trace length between C11 and pins 14 and 15 should be kept as short as possible.
In practice, VCC1, VCC, and the supply for the output stage bias will be tied to this supply line. This can be accomplished
using a suitably-long transmission line which is RF shorted on the other end. Ideally the length of this line will be a quar-
ter wavelength, but it only needs to be long enough so that the effects of other supply bypass capacitors on the inter-
stage match are minimized. If board space is a concern, this isolation can also be accomplished with an RF choke
inductor or ferrite bead. Additionally, a higher-value capacitor than shown on the application schematic can be used if
bypass capacitors must be closer. A Smith Chart can be used to provide initial guidance for value selection and parts
placement. Be aware of the self-resonant frequency (SRF) of higher-valued capacitors. The SRF must be above the fre-
quency of operation.
The output matching caps are C5, C6, and C7. These are tuned along with the 50
Ω transmission line segments TL1 and
TL2, as shown on the evaluation board schematic. These segments should be duplicated as closely as possible. Due to
variations in FR-4 characteristics and PCB manufacturer process variations, some benefit will be obtained from small
adjustments to these transmission line lengths when the evaluation board layout is duplicated on another design. Prior to
full rate manufacturing, the board layout of early prototypes should include some additional exposed ground areas
around C5, C6, and C7 to optimize this part of the circuit. In order to reduce component count, the output can also be
tuned with a single capacitor. A Smith Chart can help determine the desired value and transmission line length, which
can be similarly adjusted on the board prior to production. This will result in a slightly lower-bandwidth and more sensi-
tive match, but in most applications the bandwidth is still sufficient.
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