參數(shù)資料
型號: ICS843002CY-31T
英文描述: 700MHZ FEMTOCLOCKS⑩ VCXO BASED FREQUENCY TRANSLATOR AND JITTER ATTENUATOR
中文描述: ⑩VCXO的700MHz的FEMTOCLOCKS基于頻率轉(zhuǎn)換和抖動衰減器
文件頁數(shù): 18/27頁
文件大小: 274K
代理商: ICS843002CY-31T
843002CY-31
www.icst.com/products/hiperclocks.html
REV. B NOVEMBER 22, 2005
18
Integrated
Circuit
Systems, Inc.
ICS843002-31
700MH
Z
F
EMTO
C
LOCKS
VCXO B
ASED
F
REQUENCY
T
RANSLATOR
AND
J
ITTER
A
TTENUATOR
PRELIMINARY
C
P
=
C
S
20
N
OTES
ON
SETTING
THE
VALUE
OF
C
P
As another general rule, the following relationship should be
maintained between components C
S
and C
P
in the loop filter:
C
establishes a second pole in the VCXO PLL loop filter.
For higher damping factors (> 1), calculate the value of C
P
based on a C
value that would be used for a damping
factor of 1. This will minimize baseband peaking and loop
instability that can lead to output jitter.
C
also dampens VCXO PLL input voltage modulation by the
charge pump correction pulses. A C
value that is too low will
result in increased output phase noise at the phase detector
frequency due to this. In extreme cases where input jitter is
high, charge pump current is high, and C
is too small, the
VCXO PLL input voltage can hit the supply or ground rail
resulting in non-linear loop response.
The best way to set the value of C
is to use the filter response
software available from ICS (please refer to the following
section). C
should be increased in value until it just starts
affecting the passband peak.
N
OTES
ON
E
XTERNAL
C
RYSTAL
L
OAD
C
APACITORS
In the loop filter schematic diagram, capacitors are shown
from pin 62 to ground and pin 63 to ground. These are
optional crystal load capacitors which can be used to cen-
ter tune the external pullable crystal (the crystal frequency
can only be lowered by adding capacitance, it cannot be
raised). Note that the addition of external load capacitors
will decrease the crystal pull range and the Kvco value.
L
OOP
F
ILTER
R
ESPONSE
S
OFTWARE
Online tools to calculate loop filter response can be found at
www.icst.com.
N
OTES
ON
S
ETTING
C
HARGE
P
UMP
C
URRENT
The recommended range for the charge pump current is
50
μ
A to 500
μ
A. Below 50
μ
A, loop filter charge leakage,
due to PCB or capacitor leakage, can become a problem.
This loop filter leakage can cause locking problems, output
clock cycle slips, or low frequency phase noise.
As can be seen in the loop bandwidth and damping factor
equations or by using the filter response software available
from ICS, increasing charge pump current (I
CP
) increases
both bandwidth and damping factor.
R
T
K
E
S
I
t
n
e
r
u
C
p
m
u
P
e
g
r
a
h
C
P
C
)
6
1
A
μ
5
6
K
8
A
μ
5
2
1
K
K
4
2
A
A
μ
μ
0
0
5
0
2
5
1E-3
100E-6
10E-6
1k
10k
100k
R
SET
,
Ω
I
C
,
F
IGURE
2. C
HARGE
P
UMP
C
URRENT
VS
. V
ALUE
OF
R
SET
(
EXTERNAL
RESISTOR
) G
RAPH
C
HARGE
P
UMP
C
URRENT
, E
XAMPLE
S
ETTINGS
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