FSK datasheet(6/13 Pages) ATMEL

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4546F–RKE–12/08

T5750

Figure 4-2.

Output Power Measurement

4.4

Application Circuit

For the supply-voltage blocking capacitor C

3 a value of 68 nF/X7R is recommended (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 to realize

the Z

Load,opt by using standard valued capacitors.

1 forms together with the pins of T5750 and the PCB board wires a series resonance loop that

suppresses the 1

st harmonic, hence the position of C

1 on the PCB is important. Normally 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 value of 12 pF results for a 15 pF

load-capacitance crystal.

1 nF

1.5 pF

2.7 pF

10 nH

Rin

ANT2

ANT1

ZLopt

Power

meter

Z = 50

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