Rev. 3.5

RI-RFM-006A

Page 14 of 19

! Typical Transmitter Circuit Configuration

This RF-module IC is provided with “TXHI” and “TXLO” terminals which can drive external MOSFETs

for driving the LC serial resonance antenna circuit. This resonance antenna circuit is to send 134.2-kHz

signals to the remote TIRIS transponder. Use these terminals as illustrated below.

In this circuit configuration, by selecting a value for R1 within a range of several hundred ohms and in

accordance with the characteristics of MOSFETs (T1 and T2) and introducing the selected value, the

through current which is consumed by the MOSFETs themselves during transmission can be reduced. If

the value for R1 is too high, the on-state resistances of T1 and T2 become very high and they will have

difficulty in driving the LC resonance circuit, leading to a possible reduction of available data

communication distance. Therefore, it is recommended that the value for R1 be defined after careful

evaluation of the characteristics of T1 and T2.

L1 and C1 in the LC resonance circuit may be mutually exchanged in position without giving significant

adverse effects to the operating performance of the circuit. However, the connection as is as illustrated

above is most preferable since it reduces potential influence of high-voltage transmission signals

produced at C1 on T1 and T2, thus a higher efficiency is gained.

RI45538NS

To receiving circuit

R1

7

TXLO

8

TXHI

LC resonance circuit

GND

VCC

134.2KHz

C1

L1

T1

T2

Antenna