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When connecting the analog ground and digital ground pins of the A/D converter together, most A/D converter manufacturers would suggest: Connect the AGND and DGND pins to the same low-impedance ground through the shortest lead (Note: Because most A/D converter chips do not connect the analog ground and digital ground together, the analog and digital ground must be connected through external pins.) Any external impedance connected to DGND will pass parasitic capacitance. More digital noise is coupled to the analog circuits inside the IC. According to this recommendation, you need to connect the AGND and DGND pins of the A/D converter to the analog ground, but this method will cause problems such as whether the ground terminal of the digital signal decoupling capacitor should be connected to the analog ground or the digital ground.
If the system has only one A/D converter, the above problems can be easily solved. As shown in Figure 3, divide the ground, and connect the analog ground and digital ground together under the A/D converter. When adopting this method, it is necessary to ensure that the width of the connecting bridge between the two grounds is the same as the width of the IC, and any signal line cannot cross the division gap.
Pay attention to the following points in the design process:
1. Divide the PCB board into separate analog and digital parts.
2. Appropriate component layout.
3. A/D converters are placed across partitions.
4. Don't divide the ground. Lay a uniform ground under the analog part and the digital part of the circuit board.
5. In all layers of the circuit board, digital signals can only be routed in the digital part of the circuit board.
6. In all layers of the circuit board, the analog signal can only be routed in the analog part of the circuit board.
7. Realize the division of analog and digital power supply.
8. The wiring cannot cross the gap between the divided power planes.
9. The signal line that must cross the gap between the divided power supplies should be located on the wiring layer close to the large area ground.
10. Analyze the path and method that the return ground current actually flows through.
11. Adopt correct wiring rules
The above is the introduction of several points of attention for PCB design. Ipcb is also provided to PCB manufacturers and PCB manufacturing technology.
