参数资料
型号: MK1575-01GI
元件分类: 时钟及定时
英文描述: PLL BASED CLOCK DRIVER, 2 TRUE OUTPUT(S), 0 INVERTED OUTPUT(S), PDSO16
封装: 4.40 MM, 0.65 MM PITCH, MO-153, TSSOP-16
文件页数: 8/12页
文件大小: 217K
代理商: MK1575-01GI
CLOCK RECOVERY PLL
MDS 1575-01 L
5
Revision 070605
In te gr ated Circuit Systems 525 Ra ce Street, San Jose, CA 9512 6 tel (4 08) 297-1 201 www.icst.com
MK1575-01
Setting PLL Loop Bandwidth and
Damping Factor
The frequency response of the MK1575-01 PLL may
be approximated by the following equation:
Normalized PLL Bandwidth
The associated damping factor is calculated as follows:
Damping factor,
Where:
KO =
VCO gain in Hz/Volt
(use 340 MHz/V)
Icp =
Charge pump current, 12.5
A
N
=
Total feedback divide from VCO,
(Refer to N Value table, below)
CS =
External loop filter capacitor in Farads
RS =
Loop filter resistor in Ohms
The above bandwidth equation calculates the
“normalized” loop bandwidth which is approximately
equal to the - 3dB bandwidth. This approximate
calculation does not take into account the effects of
damping factor or the third pole imposed by CP. It does,
however, provide a useful approximation of filter
performance.
To prevent jitter on the output clocks due to modulation
of the PLL by the input reference frequency, the
following general rule should be observed:
In general, the loop damping factor should be 0.7 or
greater to ensure output stability. For video
applications, a low damping factor (0.7 to 1.0) is
generally desired for fast genlocking. For telecom
applications, a higher damping factor is usually
desirable. A higher damping factor will create less
passband gain peaking which will minimize the gain of
network clock wander amplitude. A higher damping
factor may also increase output clock jitter when there
is excess digital noise in the system application, due to
the reduced ability of the PLL to respond to, and
therefore compensate for, phase noise ingress.
Notes on setting the value of CP
As another general rule, the following relationship
should be maintained between components C1 and C2
in the external loop filter:
Where:
CB = External bypass capacitor in Farads
Note that the MK1575-01 contains an internal 300 pF
filter cap which is connected in parallel with external
device CB. This helps to reduce output clock jitter. In
some applications external device CB will not be
required.
CP establishes a second pole in the PLL loop filter. For
higher damping factors (>1), calculate the value of CP
based on a CS 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.
CP also helps to damp VCO input voltage modulation
caused by the charge pump correction pulses. A CP
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 CP is too small, the VCO
input voltage can hit the supply or ground rail resulting
in non-linear loop response.
The best way to set the value of CP is to use the
External Loop Filter Solver at
R
S
K
O
I
CP
()
2
π N
-----------------------------------------
=
ζ
R
S
2
--------
K
O
I
CP
C
S
N
-------------------------------------
=
PLL Bandwidth
f
Phase Detector
20
--------------------------------
C
P
C
S
20
------
=
C
P
C
B
300 pF
+
=
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