ATA5811 ATMEL Corporation, ATA5811 Datasheet - Page 23

• Manufacturer Part Number: ATA5811
• Description: Ata5811 Uhf Ask/fsk Transceiver
• Manufacturer: ATMEL Corporation

6. XTO
4689F–RKE–08/06
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 more than ±150 ppm at
433.92 MHz/315 MHz and up to ±118 ppm at 868.3 MHz of initial frequency error in f
done at nominal supply voltage and temperature with the control registers 2 and 3 (see
9-7 on page 36
s u p p l y v o l t a g e a n d t e m p e r a t u r e i s t h e n < ± 0 . 5 p p m . A X T O f r e q u e n c y e r r o r o f
±150 ppm/±118 ppm can hence be tolerated due to the crystal tolerance at 25°C and the toler-
ances of C
frequency at nominal supply voltage and temperature.
Over temperature and supply voltage, the XTO's additional pulling is only ±2 ppm if C
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 6-1.
With C
P ±100 ppm and with C
is P ±50 ppm.
Since typical crystals have less than ±50 ppm tolerance at 25° the compensation is not critical.
C
enter the steep region of pulling versus load capacitance where there is a risk of an unstable
oscillation.
P
m
0
=
of the XTAL has to be lower than C
is the crystal's motional, C
18 pF with a tolerance of ±17%) hence C
C
------- -
2
m
m
L1
------------------------------------------------------------ -
14 fF, C
C
and C
L1
0
+
and C
XTAL with Load Capacitance
C
and
C
LN
L2
XTO
LN
0
in series connection.
C
Table 9-10 on page
L2
–
L1
is the reference frequency FREF for the fractional-N synthesizer. When
C
1.5 pF, C
. The XTO’s gm has very low influence of less than ±2 ppm on the
C
L
L
XTAL
0
m
is the total actual load capacitance of the crystal in the circuit and con-
+
XTO
C
7 fF, C
L
0
from the nominal f
LN
the shunt and C
10
= 9 pF and C
0
6
ppm.
C
1.5 pF, C
L2
Lmin
36). The remaining local oscillator tolerance at nominal
/2 = 3.8 pF for a Pierce oscillator type in order to not
Lmin
LN
L
XTAL
LN
= 7.4 pF and C
= 7.6 pF to 10.6 pF the pulling amounts to
= 9 pF and C
C
the nominal load capacitance of the XTAL
Crystal equivalent circuit
L
is calculated using the following formula:
= C
L
m
L1
ATA5811/ATA5812
C
C
L2
m
/ (C
C
L
0
Lmax
= 7.4 pF to 10.6 pF the pulling
L1
R
+ C
m
= 10.6 pF. The XTO oscil-
L2
)
L1, 2
at pin XTAL1
XTO
. This is
m
Table
7 fF.
23