ATA8403 datasheet(6/12 Pages) ATMEL

6 / 12 page

4983A–IND–02/07

ATA8403

Figure 4-2.

Output Power Measurement

4.4

Application Circuit

A value of 68 nF/X7R is recommended for the supply-voltage blocking capacitor C

3 (see Figure

4-3 on page 7 and Figure 4-4 on page 8). C

1 and C2 are used to match the loop antenna to the

power amplifier where C

1 typically is 3.9 pF/NP0 and C2 is 1 pF/NP0. For C2, two capacitors in

series should be used to achieve a better tolerance value and to have the possibility of realizing

the Z

Load,opt using standard valued capacitors.

1, together with the pins of ATA8403 and the PCB board wires, forms a series resonance loop

that suppresses the 1

st harmonic. Therefore, the position of C

1 on the PCB is important. Nor-

mally the best suppression is achieved when C

1 is placed as close as possible to the pins ANT1

and ANT2.

The loop antenna should not exceed a width of 1.5 mm, otherwise the Q-factor of the loop

antenna is too high.

1 (≈

50 nH to 100 nH) can be printed on PCB. C

4 should be selected so that the XTO runs on

the load resonance frequency of the crystal. Normally, a 15 pF load-capacitance crystal results

in a value of 12 pF.

1 nF

1.5 pF

2.7 pF

10 nH

Rin

ANT2

ANT1

ZLopt

Power

meter

Ω

Z = 50

Ω

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