PCB News - How to connect digital ground and analog ground

General schematic diagrams and PCB designers are very controversial about how the digital ground and analog ground are connected. Each has its own method. Generally speaking, there are two methods, such as: direct connection or bridge connection, inductance or magnetic bead connection. Kind of method. First of all, let us understand why the digital-analog ground has attracted the attention of engineers. Most of them are derived from the names of the power pins and ground pins of components (such as ADC). In fact, the pin names of the analog ground and digital ground indicate the function of the internal component itself, but it does not necessarily mean that the external should act according to the internal function. There are two parts of the digital-analog circuit inside the chip. In order to prevent the digital signal from coupling to the analog circuit, the digital ground and the analog ground are separated. I personally think that it is a division, but the internal digital-analog ground is connected. I use a multimeter to measure Some chips, such as ADV7180, KS8995, TLK2541, etc., are connected internally.

Let's talk about the advantages and disadvantages of the above two digital-to-analog ground connections:
Connect with inductance or magnetic beads
As the name implies, the digital-to-analog is connected to a certain point of the PCB board with an inductor or a magnetic bead. This seems to solve the digital signal interference with the analog circuit, but it has created a new problem-EMI. When the high-frequency electrostatic discharge interference current flows through the inductor or the magnetic bead, it will produce a voltage drop across the inductor or the magnetic bead. If it is a high-voltage test, the voltage at both ends is very high and cannot be released to the end quickly, which will damage the chip. Or the device restarts.

I personally prefer direct connection or bridging. This also solves the loop problem and avoids the generation of radiation. The digital-to-analog ground is equipotential, and there is no voltage drop or is very small, so that it will not affect the equipment when doing high-voltage tests., Damage the chip. Just pay attention to reasonable partitions or trenches and bridges. The premise of this method is to do digital and analog partitions. However, the power supply must be separated. A more secure method is to use a separate power supply, but the cost is higher. Generally, a ferrite ring is used to isolate the analog power supply from the digital power supply

The above is the introduction of how the digital ground and the analog ground are connected. Ipcb is also provided to PCB manufacturers and PCB manufacturing technology.