ATA5423 ATMEL Corporation, ATA5423 Datasheet - Page 25

• Manufacturer Part Number: ATA5423
• Manufacturer: ATMEL Corporation

4. XTO
4841A–RKE–02/05
The XTO is an amplitude–regulated Pierce oscillator type with integrated load capacitances
(2
lation frequency f
designing the system in terms of receiving and transmitting frequency offset, the accuracy of the
crystal and XTO have to be considered.
The synthesizer can adjust the local oscillator frequency for the initial frequency error in f
This is done at nominal supply voltage and temperature with the control registers 2 and 3 (see
Table 7-7
and temperature is then < ±0.5 ppm. The XTO’s gm has very low influence of less than ±2 ppm
on the frequency at nominal supply voltage and temperature.
In a single channel system less than ±150 ppm should be corrected to avoid that harmonics of
the CLK output disturb the receive mode. If the CLK is not used or if it is carefully laid out on the
application PCB (as needed for multi channel systems), more than ±150 ppm can be
compensated.
Over temperature and supply voltage, the XTO's additional pulling is only ±2 ppm. The XTAL
versus temperature and its aging is then the main source of frequency error in the local
oscillator.
The XTO frequency depends on XTAL properties and the load capacitances C
and XTAL2. The pulling of f
C
found in its data sheet. C
sists of C
Figure 4-1.
With C
P ±100 ppm and with C
is P ±50 ppm.
Since typical crystals have less than ±50 ppm tolerance at 25°C, the compensation is not criti-
cal, and can in both cases be done with the ±150 ppm.
P
m
=
is the crystal's motional, C
18 pF with a tolerance of ±17%) hence C
C
------- -
2
m
m
L1
14 fF, C
and
------------------------------------------------------------ -
C
and C
0
+
XTAL with Load Capacitance
Table
C
C
LN
L2
XTO
LN
0
C
in series connection.
L1
–
is the reference frequency FREF for the fractional–N synthesizer. When
7-10). The remaining local oscillator tolerance at nominal supply voltage
1.5 pF, C
C
C
XTAL
L
L
m
0
is the total actual load capacitance of the crystal in the circuit and con-
+
XTO
7 fF, C
C
L
0
from the nominal f
LN
the shunt and C
10
= 9 pF and C
0
ATA5423/25/28/29 [Preliminary]
6
C
1.5 pF, C
ppm.
L2
Lmin
LN
L
XTAL
LN
= 9 pF and C
= 7.4 pF to 10.6 pF, the pulling amounts to
= 7.4 pF and C
the nominal load capacitance of the XTAL
is calculated using the following formula:
C
Crystal equivalent circuit
L
L
m
= C
L1
C
C
C
L2
L
m
0
/(C
= 7.4 pF to 10.6 pF, the pulling
Lmax
L1
+ C
R
m
L2
= 10.6 pF. The XTO oscil-
)
L1, 2
at pin XTAL1
XTO
25
.