TRC101 Datasheet, PDF (5/33 Pages) RF Monolithics, Inc – highly integrated single chip

These values are what the RF port pins want to “see” as an antenna load for maximum power transfer.
Antennas ideally suited for this would be a Dipole, Folded Dipole, and Loop. For all transmit antenna
applications a bias or “choke” inductor must be included since the RF outputs are open-collector type.
The matching component values for each band are given in Table 2.
Table 2.
Ref Des 315 433 868 916
C1 6.8pF 5.1pF 2.7pF 2.7pF
C2 3.9pF 2.7pF 1.2pF 1.2pF
L1
56nH 33nH 8.2nH 8.2nH
L2 390nH 390nH 100nH 100nH
L3
68nH 47nH 22nH 22nH
Antenna Design Considerations
The TRC101 was designed to drive a differential output such as a Dipole antenna or a Loop. The loop
antenna is ideally suited for applications where compact size is required. The dipole is typically not an
attractive option for compact designs due to its inherent size at resonance and distance needed away
from a ground plane to be an efficient antenna. A monopole antenna can be used with the addition of a
balun or by using the matching circuit in Figure 1.
PCB Layout Considerations
Optimal PCB layout is very 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 or 0603,
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 add 1nH of series inductance for every 0.1” of trace length.
The crystal oscillator is also affected by additional trace length as 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 allows the internal load capacitance of the chip to be more effective in
properly loading the crystal oscillator circuit.
If using an external processor, the TRC101 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. 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.
Assembly View
5