MC9S12DT256 Device User Guide — V03.07
114
The loop bandwidth f
C
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
f
C
=10kHz:
The capacitance C
s
can now be calculated as:
The capacitance C
p
should be chosen in the range of:
A.5.3.2 Jitter Information
The basic functionality of the PLL is shown in
. With each transition of the clock f
cmp
, the
deviation from the reference clock f
ref
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
f
C
2
ζ
f
ref
⋅ ⋅
π ζ
1
ζ
2
+
+
⎝
⎠
⎛
⎞
⋅
------------------------------------------
1
10
------
f
C
f
ref
4 10
⋅
--------------
ζ
0.9
=
(
)
;
<
→
<
f
C
< 25kHz
n
f
VCO
f
ref
-------------
2
synr
1
+
(
)
⋅
=
=
= 50
R
2
π
n f
C
⋅ ⋅ ⋅
K
Φ
-----------------------------
=
= 2*
π
*50*10kHz/(316.7Hz/
Ω
)
=9.9k
Ω
=~10k
Ω
C
s
2
ζ
2
⋅
π
f
C
R
⋅
⋅
----------------------
0.516
f
C
R
⋅
---------------
ζ
0.9
=
(
)
;
≈
=
= 5.19nF =~ 4.7nF
C
s
20
⁄
C
p
C
s
10
⁄
≤
≤
C
p
= 470pF
Summary of Contents for MC9S12A256
Page 3: ...MC9S12DT256 Device User Guide 9S12DT256DGV3 D V03 07 3 ...
Page 4: ...MC9S12DT256 Device User Guide 9S12DT256DGV3 D V03 07 4 ...
Page 10: ...MC9S12DT256 Device User Guide V03 07 10 ...
Page 12: ...MC9S12DT256 Device User Guide V03 07 12 ...
Page 14: ...MC9S12DT256 Device User Guide V03 07 14 Table A 21 Expanded Bus Timing Characteristics 125 ...
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Page 131: ...MC9S12DT256 Device User Guide V03 07 131 User Guide End Sheet ...
Page 132: ...MC9S12DT256 Device User Guide V03 07 132 FINAL PAGE OF 132 PAGES ...