RXC101 Datasheet, PDF (6/33 Pages) RF Monolithics, Inc – Multi-channel High data rate Programmable

The matching component values for each band are given in Table 1.
Table 1.
Band L1
315 56
433 36
868 15
916 15
C1=C2
9
7
3
3
Antenna Design Considerations
The RXC101 was designed to drive a differential output such as a Dipole antenna or a Loop. Most
compact application use the loop since it can be made small. The dipole is typically not an attractive
option for compact designs based on the fact of its inherent size at resonance and distance needed away
from a ground plane to be an efficient antenna. A monopole is possible with addition of a balun or using
the matching circuit in Figure 1.
PCB Layout Considerations
PCB layout is the most critical. For optimal transmit and receive performance, the trace lengths at the RF
pins must be kept as short as possible. Using small, surface mount components, like 0402, will yield the
best performance as well as keep the RF port compact. Make all RF connections short and direct. A
good rule of thumb to adhere to is for every 0.1” of trace length add 1nH of series inductance to the path.
The crystal oscillator is also affected by additional trace length in that it adds parasitic capacitance to the
overall load of the crystal. To minimize this effect place the crystal as close as possible to the chip and
make all connections short and direct. This will minimize the effects of “frequency pulling” that stray
capacitance may introduce and allow the internal load capacitance of the chip to be more effective in
properly loading the crystal oscillator circuit.
If using an external processor, the RXC101 provides an on-chip clock for that purpose. Even though this
is an integrated function, long runs of the clock signal may radiate and cause interference, especially if
there is no ground plane run directly under the trace. This can degrade receiver performance as well as
add harmonics or unwanted modulation to the transmitter. Keep clock connections as short as possible
and surround the clock trace with an adjacent ground plane pour where needed. This will help in
reducing any radiation or crosstalk due to long runs of the clock signal.
Good power supply bypassing is also essential. Large decoupling capacitors should be placed at the
point where power is applied to the PCB. Smaller value decoupling capacitors should then be placed at
each power point of the chip as well as bias nodes for the RF port. Poor bypassing lends itself to
conducted interference which can cause noise and spurious signals to couple into the RF sections,
significantly reducing performance.
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