Rainbow Electronics ATA8402 - Manual (Page 6)

6
4982A–IND–02/07
ATA8402
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 C
2
are used to match the loop antenna to the
power amplifier where C
1
typically is 8.2 pF/NP0 and C
2
is 6 pF/NP0 (10 pF + 15 pF in series).
For C
2
, 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.
C
1
, together with the pins of ATA8402 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.
L
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
2.2 pF
33 nH
C
1
C
2
L
1
V
S
R
in
ANT2
ANT1
Z
Lopt
Power
meter
50
Ω
Z = 50 Ω