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Application circuit, Atar862-8 – Rainbow Electronics ATAR862-8 User Manual

Page 8

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8

ATAR862-8

4589B–4BMCU–02/03

Figure 5.

Output Power Measurement

Application Circuit

For the supply-voltage blocking capacitor C

3

, a value of 68 nF/X7R is recommended

(see Figure 6 and Figure 7). C

1

and C

2

are used to match the loop antenna to the power

amplifier where C

1

typically is 3.9 pF/NP0 and C

2

is 1 pF/NP0; for C

2

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.

C

1

forms together with the pins of the PLL transmitter block and the PCB board wires a

series resonance loop that suppresses the 1

st

harmonic, thus, 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.

L

1

(

»

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

4

should be selected so 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.

~

~

ANT2

ANT1

Rin

Power

meter

L

1

= 10n

C

2

= 1.5p

Z

Lopt

V

S

Z = 50

W

50

W

C

1

= 1n

3

C = 2.7p