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The power delivery network (PDN) of a circuit board provides both power and ground to the design, and connecting the components to the PDN is one of the standard steps in PCB layout. But as signal speeds have increased, PCB PDNs have demanded more care and attention in their configuration, especially the ground plane. For good signal integrity, it is essential to lay out the design so the ground plane can provide clear return paths for digital, analog, and mixed-signal designs.
Through the years, there have been many attempts to enhance circuit board signal integrity by altering the ground planes, but that often isn't the best solution. This article will look at the problems with different ground plane configurations and some of the better alternatives. We will also list some recommendations to help with the layout of PCB grounding in mixed-signal designs.
The Question of Whether to Use Separate Ground Planes in Mixed-Signal Designs
signal intergrityAs signal speeds rose on mixed-signal circuit boards, engineers experimented with different steps to improve the signal integrity in the designs. One problem was the tendency for signal return paths in the ground plane of either digital or analog circuitry to create crosstalk in the nearby routing of the other type. To resolve this problem, designers tried splitting the ground plane into separate analog and digital planes. The thinking was that the split would solve the noise problem by isolating the circuitry into two different areas. However, it resulted in more interference problems instead.
Isolating digital and analog ground into separate planes may be helpful for designs where those areas of circuitry are entirely isolated and don't have any interaction with each other. It may also be necessary for safety if your design generates high-voltage currents from an isolated power supply. But for a standard mixed-signal design, splitting a ground plane into separate analog and digital sections can introduce new electromagnetic interference (EMI) problems.
The ground plane in a circuit board should provide clear return paths for the signals in the design. If high-speed signals are routed over an area of the board that doesn't have a ground plane adjacent to it, they will be forced to find an alternate path back to their source. Whatever alternate paths the signal returns finally use may have a large loop inductance acting like an antenna radiating EMI and ruining the signal integrity of the design. Analog signals routed across voids in the ground plane can also exhibit similar EMI problems.
Through the years, there have been many attempts to enhance circuit board signal integrity by altering the ground planes, but that often isn't the best solution. This article will look at the problems with different ground plane configurations and some of the better alternatives. We will also list some recommendations to help with the layout of PCB grounding in mixed-signal designs.
The Question of Whether to Use Separate Ground Planes in Mixed-Signal Designs
signal intergrityAs signal speeds rose on mixed-signal circuit boards, engineers experimented with different steps to improve the signal integrity in the designs. One problem was the tendency for signal return paths in the ground plane of either digital or analog circuitry to create crosstalk in the nearby routing of the other type. To resolve this problem, designers tried splitting the ground plane into separate analog and digital planes. The thinking was that the split would solve the noise problem by isolating the circuitry into two different areas. However, it resulted in more interference problems instead.
Isolating digital and analog ground into separate planes may be helpful for designs where those areas of circuitry are entirely isolated and don't have any interaction with each other. It may also be necessary for safety if your design generates high-voltage currents from an isolated power supply. But for a standard mixed-signal design, splitting a ground plane into separate analog and digital sections can introduce new electromagnetic interference (EMI) problems.
The ground plane in a circuit board should provide clear return paths for the signals in the design. If high-speed signals are routed over an area of the board that doesn't have a ground plane adjacent to it, they will be forced to find an alternate path back to their source. Whatever alternate paths the signal returns finally use may have a large loop inductance acting like an antenna radiating EMI and ruining the signal integrity of the design. Analog signals routed across voids in the ground plane can also exhibit similar EMI problems.
