ATA5429 ATMEL Corporation, ATA5429 Datasheet - Page 26

• Manufacturer Part Number: ATA5429
• Description: (ATA5423 - ATA5429) UHF ASK/FSK Transceiver
• Manufacturer: ATMEL Corporation

26
ATA5423/25/28/29 [Preliminary]
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
tance of about 2 k . The worst case for technological, temperature and supply voltage variations
is then for C
Due to the large gain at startup, 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 sets N_RESET to High and activates the CLK output
if CLK_ON in control register 3 is High (see
VSOUT and DVCC voltage also have to be fulfilled (see
To save current in IDLE and Sleep modes, the load capacitors are partially switched off in these
modes with S1 and S2, as seen in
It is recommended to use a crystal with C
C
Lower values of C
higher values of C
Re Z
1
3
3
0
0
=
consists of crystals C
= -j/(2
of the XTAL has to be lower than C
= 1.0 pF to 2.2 pF.
= -j/(2
-----------------------------------------------------------------------------------------------------------
4
XTOcore
XTO
1
, Z
2
2
= 13.5 MHz, gm = 19 mS, C
to 20
as complex impedances at pin XTAL1 and XTAL2, hence
0
=
f
2
m
2.2 pF always higher than 1.5 k
Re
f
f
XTO
C
XTO
m
m
an amplitude detector detects the oscillation amplitude and sets XTO_OK to
m
Z
----------------------------------------------------------------------------------------------------- -
1
can be used, this increases the start–up time slightly. Lower values of C
(up to 15 fF) can also be used, this has only little influence on pulling.
2
C
Re Z
Z
Z
C
0
3
0
1
L1
in parallel with an internal 110 k resistor hence
) /110 k , gm is the internal transconductance between XTAL1 and
+
+
) + 5
Z
Z
XTOcore
2
2
+
Z
Z
3
3
and Z
Figure
k
+
+
+
Z
Z
R
1
at C
1
L
m
Lmin
= 9 pF, and C
2
Z
Z
= –j/(2
4-2.
0
/2 = 3.7 pF for a Pierce oscillator type in order to not
2
2
Table
2.2 pF with this XTO. The negative resistance is
m
g
Z
= 3.0 fF to 7.0 fF, C
m
3
7-7). Note that the necessary conditions of the
g
m
0
= 2.2 pF, this results in a negative resis-
f
XTO
Figure 4-2
C
L2
) + 5 .
and
LN
= 9 pF, R
Figure
5-1).
m
4841A–RKE–02/05
< 120
and
0
or