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FS6128-01 Datasheet(PDF) 2 Page - List of Unclassifed Manufacturers

No. de Pieza. FS6128-01
Descripción  PLL Clock Generator IC with VCXO
Descarga  7 Pages
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Fabricante  ETC1 [List of Unclassifed Manufacturers]
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FS6128-01 Datasheet(HTML) 2 Page - List of Unclassifed Manufacturers

   
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AMERICAN MICROSYSTEMS, INC.
April 2000
2
4.24.00
FS6128-01
FS6128-01
FS6128-01
FS6128-01
PLL Clock Generator IC with VCXO
PLL Clock Generator IC with VCXO
PLL Clock Generator IC with VCXO
PLL Clock Generator IC with VCXO
ISO9001
ISO9001
ISO9001
ISO9001
Table 2: Pin Descriptions
Key: AI = Analog Input; AO = Analog Output; DI = Digital Input; DI
U = Input with Internal Pull-Up; DI
D = Input with Internal Pull-Down; DIO = Digital Input/Output; DI-3 = Three-Level Digital Input,
DO = Digital Output; P = Power/Ground; # = Active Low pin
PIN
TYPE
NAME
DESCRIPTION
1
AI
XIN
VCXO Feedback
2
P
VDD
Power Supply (+3.3V)
3
AI
XTUNE
VCXO Tune
4
P
VSS
Ground
5
DO
CLK
Clock Output
6
-
n/c
No Connection
7
DO
VSS
Ground
8
AO
XOUT
VCXO Drive
3.0
Functional Block Description
3.1
Phase-Locked Loop (PLL)
The on-chip PLL is a standard frequency- and phase-
locked loop architecture. The PLL multiplies the reference
oscillator to the desired frequency by a ratio of integers.
The frequency multiplication is exact with a zero synthe-
sis error.
3.2
Voltage-Controlled Crystal
Oscillator (VCXO)
The VCXO provides a tunable, low-jitter frequency refer-
ence for the rest of the FS6128 system components.
Loading capacitance for the crystal is internal to the
FS6128. No external components (other than the reso-
nator itself) are required for operation of the VCXO.
Continuous fine-tuning of the VCXO frequency is accom-
plished by varying the voltage on the XTUNE pin. The
value of this voltage controls the effective capacitance
presented by the VCXO to the crystal.
When using a crystal with a VCXO, it is important that the
crystal load capacitance (as specified in Table 4: Oper-
ating Conditions be matched to the load capacitance as
presented by the VCXO. The crystal must be specified
with the correct load capacitance to obtain the maximum
tuning range.
The oscillator operates the crystal resonator in the paral-
lel-resonant mode. Crystal warping, or the “pulling” of the
crystal oscillation frequency, is accomplished by altering
the effective load capacitance presented to the crystal by
the oscillator circuit. The actual amount that changing the
load capacitance alters the oscillator frequency will be
dependent on the characteristics of the crystal as well as
the oscillator circuit itself.
Specifically, the motional capacitance of the crystal (usu-
ally referred to by crystal manufacturers as C1), the static
capacitance of the crystal (C0), and the load capacitance
(CL) of the oscillator determine the warping capability of
the crystal in the oscillator circuit.
A simple formula to obtain the warping capability of a
crystal oscillator is:
()
() (
)
C
C
C
C
C
C
C
ppm
f
L
L
L
L
1
0
2
0
6
1
2
1
2
10
)
(
+
×
+
×
×
×
=
where CL1 and CL2 are the two extremes of the applied
load capacitance.
EXAMPLE:
A crystal with the following parameters is
used. With C1 = 0.02pF, C0 = 5pF, CL1 = 13pF, and CL2
=35pF, the coarse tuning range is
()
() (
)
ppm
.
f
305
13
5
35
5
2
106
13
35
02
0
+
×
+
×
×
×
=
.


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