- on Do 28 Mai 2015
Bead and Cap.for Power Supply
一般每个电源，一个bead！ 一个input，一个电容！
- When we use MULTI-LAYER e.g 4 layer, then it is better to use this form because we can get the certain voltage whereve we want and the compenents can be distributed everywhere in the Board:
- when we use only 2 layer, it's better to use the normal form
TXB0108 is used as a Buffer and thus power supply of both side A and B can share the same Bead.
CORRECT:
WRONG:
Disscuss about the Ferrite Bead
Ferrite Bead is almost like a Conductor. So it can combine with a capacity to elimite the noise of power supply and low the insertion loss of signal.
When capacitors and inductors are combined as seen in > Figure 2-9 (b) and (c), the slope for the characteristics curve of insertion loss can be made more acute compared with using only a capacitor as in (a). Since the insertion loss in the decay area can be increased simultaneously this way, it is more advantageous when the noise must be greatly attenuated.Since, in Figure 2-9, the IC ground and the ground for the closest capacitor become return paths for the noise, they should be made as short as possible to minimize impedance. Also when a π-section filter is formed as shown in Figure 2-9 (c), it is more desirable to use a ground separate to the capacitor (with a via, etc.) so as to prevent noise from bypassing the inductor (when conditions of the grounds are not desirable) going through the ground (the ground plane is shared, however). The decoupling circuit shown in Figure 2-9 can be applied to noise entering from outside, in addition to noise emitted by the IC. For example, with circuits exposed to strong high frequency energy such as those in mobile phones, a decoupling circuit with capacitor and inductor combination to achieve larger insertion loss is more suitable.
Analyse:
LC Filter Circuit
how to calucate the L value????
e.g. decoupling Cap. is 100 nF
100欧 @100Mhz
100欧表示感抗，|Z|
Xl= jwl ;
w=2pif;
故
差分布线
开始需要在节点先用单线引出来一点，然后在布线
致命错误！！！！ 不能直接倒置元器件！ 因为实物是不能倒置或者对称镜像表示的