RF2163
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 applications
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-block-
ing 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, interstage and out-
put 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 cir-
cuit 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 quarter wavelength,
but it only needs to be long enough so that the effects of other supply bypass capacitors on the interstage match are mini-
mized. If board space is a concern, this isolation can also be accomplished with an RF choke inductor or ferrite bead. Addition-
ally, 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 fre-
quency (SRF) of higher-valued capacitors. The SRF must be above the frequency of operation.
The output matching caps are C5, C6, and C7. These are tuned along with the 50Ω 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 pro-
duction. This will result in a slightly lower-bandwidth and more sensitive match, but in most applications the bandwidth is still
sufficient.
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support, contact RFMD at (+1) 336-678-5570 or sales-support@rfmd.com.
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