Have hardware engineers encountered these crystal oscillator circuit design problems? Wiring, capacitance matching, interference prevention, etc. The manufacturer provides you with some basic design requirements for SMD crystal oscillator schematic diagram. If the following requirements are met, you can basically design a suitable SMD crystal oscillator schematic diagram!
- In PCB design, the shell of quartz crystal must be grounded to prevent the yearning radiation of crystal oscillator and shield external interference. The floor under the crystal oscillator shall be paved to prevent interference with other layers. Because some engineers do not pave the floor at the top and bottom layers when laying multilayer boards, but they suggest the floor where the crystal oscillator is located.
- Decoupling of SMD crystal oscillator power supply is very important. It is recommended to add magnetic beads, select three decoupling capacitors, and reduce the capacitance. The clock output pin is matched. The specific matching resistance can be determined according to the test results.
- No wiring is allowed under the crystal oscillator, and no wiring and other components are allowed within the range of 5mm around, mainly to prevent quartz crystal from interfering with other wiring and components.
- After adding a capacitor, the capacitance value should be small (what results can be achieved if it is increased, you can try it), forming a first level low-pass filter. The selection of resistance and capacitance depends on the specific test results.
- Of course, the clock line should be as short as possible. If you don’t want the clock cable to interfere with all the way, let’s cut it short.
- The quartz crystal resonator should not be placed on the edge of the board. For safety reasons, the ground of the board is often connected to the metal shell or mechanical structure. This ground is temporarily called the reference ground plate. If the crystal cloth is placed on the edge of the board, the crystal oscillator and the reference ground plate will form an electric field distribution. There are often many cables at the edge of the board. When the cables pass through the crystal oscillator and the reference ground plate, the electric field is, The cable is disturbed.
- The electric field distribution of the chip crystal oscillator and the reference ground plate is separated by the GND of the PCB at the place far from the edge of the crystal cloth, and the electric field distributed to the reference ground plate is greatly reduced