參數(shù)資料
型號: MC9S12DG256MPVE
廠商: FREESCALE SEMICONDUCTOR INC
元件分類: 微控制器/微處理器
英文描述: 16-BIT, FLASH, 25 MHz, MICROCONTROLLER, PQFP112
封裝: LQFP-112
文件頁數(shù): 18/132頁
文件大?。?/td> 782K
代理商: MC9S12DG256MPVE
MC9S12DT256 Device User Guide — V03.07
114
The loop bandwidth fC should be chosen to fulfill the Gardner’s stability criteria by at least a factor of 10,
typical values are 50.
ζ = 0.9 ensures a good transient response.
And finally the frequency relationship is defined as
With the above values the resistance can be calculated. The example is shown for a loop bandwidth
fC=10kHz:
The capacitance Cs can now be calculated as:
The capacitance Cp should be chosen in the range of:
A.5.3.2 Jitter Information
The basic functionality of the PLL is shown in
Figure A-3. With each transition of the clock f
cmp, the
deviation from the reference clock fref is measured and input voltage to the VCO is adjusted
accordingly.The adjustment is done continuously with no abrupt changes in the clock output frequency.
Noise, voltage, temperature and other factors cause slight variations in the control loop resulting in a clock
jitter. This jitter affects the real minimum and maximum clock periods as illustrated in
fC
2
ζ fref
πζ
1
ζ
2
+
------------------------------------------ 1
10
------
fC
fref
410
--------------
ζ 0.9
=
()
;
<
<
fC < 25kHz
n
fVCO
fref
-------------
2 synr 1
+
()
==
= 50
R
2
π nfC
KΦ
-----------------------------
=
=2*
π*50*10kHz/(316.7Hz/)=9.9k=~10k
Cs
2
ζ
2
π fC R
----------------------
0.516
fC R
---------------
ζ 0.9
=
()
;
=
= 5.19nF =~ 4.7nF
Cs 20
Cp Cs 10
≤≤
Cp = 470pF
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