11640-823 データシートの表示（PDF） - AMI Semiconductor
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11640-823 Datasheet PDF : 6 Pages
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FS6146
VCXO Clock Generator IC
Table 2: Pin Descriptions
Key: AI = Analog Input; AO = Analog Output; DI = Digital Input; DIU = Input with Internal Pull-Up; DID = 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 Crystal Feedback
2
AO
XOUT / FREF VCXO Crystal Drive / External Reference Clock Input
3
P
VDD
Core Power Supply
4
AI
XTUNE
VCXO Tune Input
5
P
VSS
Ground
6
-
N/C
No Connection
7
DIU
OE
Output Enable
8
DO
CLKA
Clock Output “A”
9
-
N/C
No Connection
10
-
N/C
No Connection
11
DO
CLKB
Clock Output “B”
12
P
VSS
Ground
13
P
VDDO
Output Power Supply (must be less than or equal to VDD)
14
-
N/C
No Connection
15
-
N/C
No Connection
16
-
N/C
No Connection
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 FS6146 system components.
Loading capacitance for the crystal is internal to the
FS6146. No external components (other than the crystal
resonator 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 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” or “pulling”
capability of the crystal in the oscillator circuit.
A simple formula to obtain the warping capability of a
crystal oscillator is:
∆f
(
ppm)
=
C1 × (C L2 − C )L1 ×106
2 × (C0 + C L2)× (C0 + C )L1
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 = 10pF, and CL2 =
22.66pF, the tuning range is
∆f
=
0.02 × (22.66 −10)×106
2 × (5 + 22.66)× (5 + 10)
= 305 ppm .
2
ISO9001
2.27.02
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