Rev. 3.5

RI-RFM-006A

Page 17 of 19

! Precautions for Mounting and Actual Use

Described in this section are the precautions to be taken at mounting and actual use of the RI-RFM-006A

while designing and manufacturing a TIRIS Read-Write System using this IC, especially, critical issues

as may affect the operating performance of the IC and, in particular, the system communication

performance with a remote TIRIS transponder.

1. Power Supply Line

When the signals returned from a remote TIRIS transponder are amplified by sequentially using the three

CMOS inverter type amplifiers incorporated in this RF-module IC, an undesirable feedback loop is

formed from the third amplifier toward the first one through parasitic L, R and C whose formation is not

avoidable because of the structure of this IC and its internal power supply line (see the diagram below) as

CMOS devices are inevitably bi-directional. If this feedback loop is left as is, it normally leads to an

oscillation; particularly, when the frequency band of each amplifier is limited so that it matches that of

the transponder return signals, oscillation occurs at a frequency within this band which counts on high

gains from the very nature of things, in consequence, adversely affecting the demodulating performance

of the received FSK signals.

Equivalent circuit for internal power supply line feedback loop

This situation does not a little occur when a multiple number of high-gain amplifiers are integrated in a

CMOS device. Formation of this undesirable feedback loop in the amplifier band can be avoided by

minimizing the impedance of the power supply line through optimization of the printed circuit boards and

using a suitable bypass capacitor. It is extremely difficult to obtain true values for these parasitic L, R and

C forming the internal power supply line feedback loop, but it can be said from the empirical viewpoint

that it is possible to inhibit the said oscillation using a bypass capacitor with a capacity of

1

µF and having a sufficiently low impedance within the said amplifier frequency band provided that

appropriate wiring patterns are defined for the power supply line on the printed circuit boards and in the

peripheries of external parts for the amplifiers.

Positive power supply (Vcc) line

Feedback loop

Bypass capacitor

From Antenna

1

2

3

4

5

6

16

15

14

13

12

11

Amplifier 1

Amplifier 2

Amplifier 3

Internal power supply line