ATA5823 ATMEL Corporation, ATA5823 Datasheet - Page 28

• Manufacturer Part Number: ATA5823
• Description: Uhf Ask/fsk Transceiver Ata5823 Ata5824
• Manufacturer: ATMEL Corporation

28
ATA5823/ATA5824
Figure 9-1.
With C
P ±100 ppm and with C
is P
Since typical crystals have less than ±50 ppm tolerance at 25°C, the compensation is not critical
and can, in both cases, be done with the ±150 ppm.
C
enter the steep region of pulling versus load capacitance where there is a risk of an unstable
oscillation.
To ensure proper start-up behavior the small signal gain, and thus the negative resistance pro-
vided by this XTO at start is very large. For example oscillation starts up, even in worst case,
with a crystal series resistance of 1.5
approximately given by
with Z
Z
Z
Z
XTAL2 with typically 19 ms at 25°C.
With f
about 2 k . The worst case for technological, supply voltage and temperature variations is then
for C
Due to the large gain at start, the XTO is able to meet a very low start-up time. The oscillation
start-up time can be estimated with the time constant
After 10
High if the amplitude is large enough. This activates the CLK output if CLK_ON and CLK_EN in
control register 3 are High (see
the DVCC voltage also have to be fulfilled (see
31).
Re Z
1
3
3
0
=
=
consists of crystals C
=
of the XTAL has to be lower than C
-----------------------------------------------------------------------------------------------------------
4
XTOcore
–
–
0
XTO
1
j/(2
j/(2
±
, Z
m
50 ppm.
2.2 pF always higher than 1.5 k
2
= 13.5 MHz, gm = 19 ms, C
2
to 20 , an amplitude detector detects the oscillation amplitude and sets XTO_OK to
14 fF, C
as complex impedances at pin XTAL1 and XTAL2 hence
=
f
2
m
XTAL with Load Capacitances
Re
f
f
XTO
C
XTO
m
C
Z
----------------------------------------------------------------------------------------------------- -
0
L1
1
2
1.5 pF, C
C
C
Re Z
Z
Z
XTAL
0
3
1
L1
0
m
in parallel with an internal 110 k resistor hence
) /110 k , gm is the internal transconductance between XTAL1 and
+
+
) + 5 and Z
Z
Z
XTOcore
7 fF, C
2
2
+
Table 12-12 on page
Z
LN
Z
3
3
+
+
= 9 pF and C
0
+
Z
C
Z
L
R
k
1
L2
1
= 9 pF, C
1.5 pF, C
m
Lmin
2
=
at C
Z
Z
/2 = 3.7 pF for a Pierce oscillator type in order to not
2
2
–
j/(2
0
g
Z
m
2.2 pF with this XTO. The negative resistance is
3
Figure 9-2 on page 29
0
LN
L
= 2.2 pF this results in a negative resistance of
= 7.4 pF to 10.6 pF the pulling amounts to
= 9 pF and C
g
m
Crystal equivalent circuit
C
39). Note that the necessary conditions of
f
L
XTO
= C
L
m
L1
C
C
C
C
L2
L2
m
0
/(C
L
) + 5 .
= 7.4 pF to 10.6 pF the pulling
L1
+ C
R
m
L2
and
)
Figure 10-1 on page
4829D–RKE–06/06