參數(shù)資料
型號: ICS663MT
英文描述: PLL BUILDING BLOCK
中文描述: 鎖相環(huán)積木
文件頁數(shù): 6/7頁
文件大?。?/td> 146K
代理商: ICS663MT
PLL B
UILDING
B
LOCK
MDS 663 D
6
Revision 062904
Integrated Circuit Systems
525 Race Street, San Jose, CA 95126
tel (408) 297-1201
www.icst.com
ICS663
Determining the Loop Filter Values
The loop filter components consist of C
1
, C
2
, and R
Z
.
Calculating these values is best illustrated by an
example. Using the example in Figure 1, we can
synthesize 20 MHz from a 200 kHz input.
The phase locked loop may be approximately
described by the following equations:
Bandwidth
Damping factor,
where:
K
O
= VCO gain (MHz/Volt)
I
cp
= Charge pump current (
μ
A)
N = Total feedback divide from VCO,
including the internal VCO post divider
C
1
= Loop filter capacitor (Farads)
R
Z
= Loop filter resistor (Ohms)
As a general rule, the bandwidth should be at least 20
times less than the reference frequency, i.e.,
In this example, using the above equation, bandwidth
should be less than or equal to 10 kHz. By setting the
bandwith to 10kHz and using the first equation, R
Z
can
be determined since all other variables are known. In
the example of Figure 1, N = 200, comprising the divide
by 2 on the chip (VCO post divider) and the external
divide by 100. Therefore, the bandwidth equation
becomes:
R
200 2.5
2
π
200
and R
Z
= 25 k
Choosing a damping factor of 0.7 (a minimal damping
factor than can be used to ensure fast lock time),
damping factor equation becomes:
and C
1
= 1.25 nF (1.2 nF is the nearest standard
value).
The capacitor C
2
is used to damp transients from the
charge pump and should be approximately 1/20th the
size of C
1
, i.e.,
Therefore, C
2
= 60 pF (56 pF nearest standard value).
To summarize, the loop filter components are:
C
1
= 1.2 nf
C
2
= 56 pf
R
z
= 25 k
R
K
I
2
π
N
------------------------------------
)
=
ζ
R
Z
2
------
K
I
C
1
N
------------------------------
=
BW
REFIN
(
)
20
10,000
-------------------------------
=
0.7
25 000
2
-----------------
200 2.5 C
1
200
--------------------------------
=
C
2
C
1
20
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PDF描述
ICS664-01 Digital Video Clock Source
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ICS664G-01T Digital Video Clock Source
ICS664-02 PECL Digital Video Clock Source
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ICS664-03 制造商:ICS 制造商全稱:ICS 功能描述:Digital Video Clock Source
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