MRF24J40 datasheet(49/66 Pages) MICROCHIP

49 / 66 page

Advance Information

DS39776A-page 47

MRF24J40

APPENDIX A:

LAYOUT AND PART

SELECTION

A.1

Layout Considerations and RF

Measurements

Below is an example of the circuit diagram of a balun.

A balun is the impedance transformer from unbalanced

input of the PCB antenna and the balanced input of the

RF transceiver (pins RFP and RFN).

Figure A-2 shows the measured impedance of the

balun where the center of the band is very close to 50

Ω.

When using low tolerance components (i.e., ±5%)

along with an appropriate ground, the impedance will

remain close to the 50

Ω measurement. Figure A-3

shows the measured impedance of the PCB antenna

using a logarithmic scale magnitude. Figure A-4 shows

the same impedance using a Smith Chart diagram and

Figure A-5 using a voltage standing wave ratio.

FIGURE A-1:

EXAMPLE CIRCUIT DIAGRAM

FIGURE A-2:

MEASURED IMPEDANCE

ANT

0.3 pF

4.7 nH

0.5 pF

C38

0.5 pF

5.6 nH

C43

0.5 pF

C40

100 nF

0.5 pF

RFP

RFN

10 nH

C23

C37

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