ATA5746 ATMEL Corporation, ATA5746 Datasheet - Page 15

• Manufacturer Part Number: ATA5746
• Description: (ATA5745 / ATA5746) UHF ASK/FSK Receiver
• Manufacturer: ATMEL Corporation

4596A–RKE–05/06
Figure 3-1.
With C
P ≤±1 ppm.
The C
not enter the steep region of pulling versus load capacitance where there is risk of an unstable
oscillation.
To ensure proper start-up behavior, the small signal gain and the negative resistance provided
by this XTO at start is very large. For example, oscillation starts up even in the worst case with a
crystal series resistance of 1.5 kΩ at C
approximately given by
with Z
Z
Z
Z
XTAL2, with typically 20 mS at 25°C.
With f
tance of about 2 kΩ. The worst case for technology, supply voltage, and temperature variations
is then always higher than 1.4 kΩ 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 τ .
After 10τ to 20τ , an amplitude detector detects the oscillation amplitude and sets XTO_OK to
High if the amplitude is large enough; this activates the CLK_OUT output if it is enabled via the
pins CLK_OUT_CTRL0 and CLK_OUT_CTRL1. Note that the necessary conditions of the
DVCC voltage also have to be fulfilled.
It is recommended to use a crystal with C
C
Re Zxtocore
τ
1
3
3
0
=
{
= –j / (2 × p × f
consists of crystal C
= –j / (2 × p × f
= 1.0 pF to 2.2 pF.
------------------------------------------------------------------------------------------------------------------ -
4
XTO
1
0
×
and Z
m
of the XTAL has to be lower than C
π
2
≤10 fF, C
= 13.5 MHz, gm = 20 mS, C
×
}
f
=
2
XTAL
Crystal Equivalent Circuit
as complex impedances at pins XTAL1 and XTAL2, hence
Re
2
⎧
⎨
⎩
XTO
XTO
×
Z
---------------------------------------------------------------------------------------- -
0
C
1
C
≥ 1.0 pF, C
L1
Z
×
× C
× C
m
1
0
2
Z
×
+
in parallel with an internal 110-kΩ resistor, hence
XTAL
3
Z
L1
0
(
+
) / 110 kΩ, gm is the internal transconductance between XTAL1 and
Re Z
2
) + 5Ω and Z
Z
+
2
(
Z
×
3
xtocore
Z
+
LN
ATA5745/ATA5746 [Preliminary]
3
Z
+
1
= 9 pF and C
)
Z
×
C
L
+
1
0
L2
Z
= 9 pF, and C
×
R
2
≤2.2 pF.
2
0
m
= –j / (2 × p × f
Z
×
Lmin
≤2.2 pF with this XTO. The negative resistance is
)
3
gm
×
m
gm
/ 2 = 7.9 pF for a Pierce oscillator type in order to
= 3.0 fF to 10 fF, C
⎫
⎬
⎭
L1,2
C
Crystal Equivalent Circuit
L
0
= C
= 16 pF ±1%, the pulling amounts to
= 2.2 pF, this results in a negative resis-
L
m
XTO
L1
× C
× C
C
L2
m
/ (C
C
L2
0
L1
) + 5Ω.
R
+ C
LN
m
L2
= 9 pF, R
)
m
< 120Ω and
15