ATA5749 ATMEL Corporation, ATA5749 Datasheet - Page 8

• Manufacturer Part Number: ATA5749
• Description: Fractional-n PLL Transmitter IC
• Manufacturer: ATMEL Corporation

4.1.1
8
ATA5749 [Preliminary]
Antenna Impedance Matching
The PCB loop antenna should not exceed a trace width of 1.5 mm otherwise the Q-factor of the
loop antenna is too high. C4 and C5 should be selected so that the XTO runs on the load reso-
nance frequency of the crystal. A crystal with a load capacitance of 9 pF is recommended for
proper start-up behavior and low current consumption. When determining values for C4 and C5,
a parasitic capacitance of 3 pF should be included. With value of 15 pF for C4 and C5, an effec-
tive load capacitance of 9 pF can be achieved e.g. 9 pF = (15 pF + 3 pF)/2. The supply V
typically delivered from a single Li-Cell.
The maximum output power is achieved by using load impedances according to
Table 4-2 on page 9
ance seen from the ATA5749 ANT1, ANT2 into the matching network. This is not the output
impedance of the IC but essentially the peak voltage divided by the peak current with some addi-
tional parasitic effects (Cpar).
C3 in
Figure 4-2
4-3 on page 10
4-2 on page 9
els. For reference, Z
the matching network.
Figure 4-2.
Figure
is the circuit that was used to obtain the typical output power measurements in
4-2, which is an option for better matching at low power steps.
Output Power Measurement Circuit
provide recommended values and performance info at various output power lev-
and typical current consumption in
Power Meter
LOPT
50
and the output power. The load impedance Z
is defined as the impedance seen from the ATA5749 ANT1, ANT2 into
Table 4-1
C3
C2
VS
and
Z
L1
LOPT
Table 4-2
ANT2
ANT1
Figure 4-4 on page
C1
4
5
do not contain information pertaining to
PA
LOPT
is defined as the imped-
10.
Table 4-1
Table 4-1
9128C–RKE–10/08
and
Figure
Table
and
S
is