The elements for Printed Circuit Board (PCB) layout
(1 ) the components the layout of , the should be each other about components as much as possible there was not recently, for example , clock generator, crystal oscillator , CPU 's clock input are easy to produce noise in placed the time they should be near More. For those prone to noise device , low current circuit, high current circuit switching circuit , as far as possible away from microcontroller the logic control circuit and memory circuits (ROM, RAM), if possible , can be these circuits other made of Circuit boards, it is a good anti-jamming , to improve the circuit the availability * of .
(2 ) as the critical components, such as ROM, RAM and other chip next to install decoupling capacitors . In fact, the printed circuit board traces , pin connection and wiring and so may contain large inductance effects. Large inductance may Vcc traces cause severe switching noise spikes. Prevent Vcc go online switching noise spikes the only way is to VCC and the power to between the be placed one 0.1uF the electronic decoupling capacitors. If the circuit board using surface mount components, can be used chip capacitors directly bear * the components in the Vcc pin fixed. It is best to use ceramic capacitors , this is because the capacitor has a low static losses (ESL) and high frequency impedance, other this capacitor temperature and time on the media stability is also very good. Do not use tantalum capacitors , because at high frequencies it is the impedance higher.
in place Decoupling capacitor to note the following:
In the printed circuit board power input jumper 100uF around electrolytic capacitor , if the volume permitting, large capacity a number is better.
In principle, each integrated circuit chips next to are to be placed a 0.01uF ceramic capacitor , if the circuit board the gap is too small placed no less than , you can every 10 chip about to place a 1 to 10 of tantalum capacitors.
The anti-interference ability weak , off when the current changes large the components and RAM, ROM and other storage devices , should be power lines (Vcc) and ground between the access decoupling capacitors.
Capacitance of the lead is not too long , especially high frequency bypass capacitor not with a leads .
(3 ) In the SCM control system, ground types of there are many , in a systematic manner , the shield , the logic , the analog ground , etc. , ground whether the layout is reasonable , will determine the the board anti-jamming capability .
in the design Ground and ground , it should consider the following questions:
Logic and analog ground to separate the wiring, can not be combined , to their respective ground were with the corresponding power supply ground connected . In the design, analog ground should be bold , and try to increase the terminal area with the ground . In general, the input and output of the analog signal , the microcontroller circuit between preferably via optocouplers isolation .
in the design of Logic circuits printed circuit version, the ground shall constitute a closed form, to improve the circuit 's noise immunity.
Ground Should be Coarse . If the ground is very thin , then the ground resistance will be greater , resulting in ground potential with the current changes , resulting in signal level instability , leading to circuit anti-interference decline in . In the wiring space permitting , to ensure that the main ground the width of at least 2 ~ 3mm above devices pin the ground should be 1.5mm around .