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參數(shù)資料
| 型號： | C166 |
| 廠商： | SIEMENS AG |
| 元件分類： | 8位微控制器 |
| 英文描述： | 8-Bit Microcontroller(8位微控制器) |
| 中文描述： | 8位微控制器（8位微控制器） |
| 文件頁數(shù)： | 21/45頁 |
| 文件大?。?/td> | 654K |
| 代理商： | C166 |
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AP242005 07.99
Crystal Oscillators of the
C500 / C166 Microcontroller Family
7
Oscillator Circuitry Layout Recommendations
The layout of the oscillator circuit is important for the RF and EMC behavior of the design. The use
of this recommendation can help to reduce problems caused by the layout. This design
recommendation is optimized on EMC aspects.
For an optimal layout the following items have to be noted:
7.1
Avoid Capacitive Coupling
The crosstalk between oscillator signals and others has to be minimized. Sensitive inputs have to
be separated from outputs with a high amplitude.
Note: The crosstalk between different layers also has to be analyzed.
7.2
Ground Connection of the Crystal Package
The connection of the crystal package to the ground plane directly underneath the crystal and to the
ground layer via an interlayer connection has the following advantages:
The crystal metal package reduces the electromagnetic emission.
The mechanical stability of the crystal can be increased.
The ground layer and the additional ground plane underneath the crystal shield the oscillator. This
shielding decouples all signals on the other PCB side.
7.3
Avoid Parallel Tracks of High Frequency Signals
In order to reduce the crosstalk caused by capacitive or inductive coupling, tracks of high frequency
signals should not be routed in parallel (also not on different layers!).
7.4
Ground Supply
The ground supply must be realized on the base of a low impedance. The impedance can be made
smaller by using thick and wide ground tracks. Ground loops have to be avoided, because they are
working like antennas.
Note: The connection to the ground should be done with a top-pin-clip because the heat of
soldering can damage the quartz crystal.
7.5
Noise Reduction on Ground of the Load Capacitors
Noise on the ground track between the load capacitors and the on-chip oscillator ground can have
an influence on the duty cycle. This is important for systems running in direct drive mode (oscillator
frequency is equal to CPU frequency). Therefore the ground connection of the decoupling
capacitance C
B
(between
V
DD
and
V
SS
of the on-chip oscillator-Inverter) should be between
V
SS
and
system ground connection, to suppress noise from system ground, see figure 9.
7.6
Correct Module Placement
Other RF modules should not be placed near the oscillator circuitry in order to prevent them from
influencing the crystal functionality.
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