MRF24J40-I MICROCHIP [Microchip Technology], MRF24J40-I Datasheet - Page 49

• Manufacturer Part Number: MRF24J40-I
• Manufacturer: MICROCHIP [Microchip Technology]

APPENDIX A:
A.1
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-1:
FIGURE A-2:
© 2006 Microchip Technology Inc.
Layout Considerations and RF
Measurements
MEASURED IMPEDANCE
EXAMPLE CIRCUIT DIAGRAM
ANT
0.3 pF
LAYOUT AND PART
SELECTION
C7
4.7 nH
L1
0.5 pF
C23
Advance Information
0.5 pF
C38
Figure A-2 shows the measured impedance of the
balun where the center of the band is very close to 50Ω.
When using low tolerance components (i.e., ±5%)
along with an appropriate ground, the impedance will
remain close to the 50Ω 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.
0.5 pF
10 nH
5.6 nH
C43
L3
L4
L5
10 nH
0.5 pF
C37
100 nF
C40
MRF24J40
RFP
RFN
DS39776A-page 47