Rainbow Electronics ATA5757 - Manual (Page 11)

11
ATA5756/ATA5757 [Preliminary]
4702D–RKE–02/04
Application Circuits For the supply voltage blocking capacitor C
3
, a value of 68 nF/X7R is recommended
(see Figure 10 on page 12 and Figure 11 on page 13). C
1
and C
2
are used to match the
loop antenna to the power amplifier. For C
2
, two capacitors in series should be used to
achieve a better tolerance value and to enable it to realize Z
Load,opt
by using capacitors
with standard values.
Together with the pins of ATA5756 and the PCB board wires, C
1 forms
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.
L
1
(50 nH to 100 nH) can be printed on the PCB. C
4
should be selected so that the XTO
runs on the load resonance frequency of the crystal. Normally, a value of 10 pF results
in a 12 pF load-capacitance crystal due to the board parasitic capacitances and the
inductive impedance of the XTO1 pin.