CF45538NSRG4 Datasheet, PDF (17/19 Pages) Texas Instruments – TIRIS RF-Module IC for Automotive

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Precautions for Mounting and Actual Use
14.2 Wiring for Antenna Circuit
As previously described, the FSK signals sent from a remote TIRIS transponder are normally found within
a band of 120 kHz to 140 kHz. Therefore, the signal receiving circuit of this TIRIS Transmitter- Receiver
System is designed so that the signal amplification factor is necessarily highest within this band. Because
of this, all signals and noises which are produced by other devices and whose frequencies fall within this
band greatly affect the system performance, especially, its available data communication distance with the
remote TIRIS transponder among others.
In the same way, they have quite the undesirable effect not only upon the environment in which the proper
antenna for the system is found, but also upon the wire used to connect it with the IC’s “A1IN” pin which
works as the first-phase amplifier for received signals. Furthermore, if there are wires for square or pulse
wave logic signals containing high-frequency components (even though their fundamental frequencies are
low) very close to this antenna connection wire, the system’s available data communication distance with
the remote TIRIS transponder is further shortened due to the adverse effects of such wires. For all that, if
there is no other alternative than to use a long wiring between the IC and its external antenna, it is
suggested that a shielded wire be used for antenna wiring in either way as illustrated below. With this, the
antenna wiring will be less susceptible to the aforementioned adverse effects.
RI45538NS
TXLO TXHI
Antenna
7
8
Shielded wire
To receiver amplifier
Antenna resonance capacitor
RI45538NS
TXLO
7
TXHI
8
a. When the antenna is driven first.
Antenna resonance capacitor
Shielded wire
Antenna
To receiver amplifier
b. When the capacitor is driven first.
SCBU036 – December 1996
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TIRIS RF-Module IC for Automotive
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