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Single-Point and Multipoint Grounding in Circuit Boards

Key Takeaways

  • Grounding in signal boards can be classified as single-point grounding, multipoint grounding, hybrid grounding, or floating grounding.

  • Single-point grounding is the preferred grounding technique in low-frequency analog circuits. 

  • Multipoint grounding is suitable for high-frequency circuits and high-speed digital circuits. 

Circuit graphic

Grounding is a way to protect circuits from issues due to short circuit currents, electric shocks, and interference. In systematic circuit design, grounding is critical to achieving signal integrity, as it provides the return path for currents in the circuit. 

With proper grounding, a circuit can withstand electrostatic discharges, short circuit currents, and minimize noise. Grounding in signal boards can be classified into the following categories: 

  1. Single-point grounding

  2. Multipoint grounding

  3. Hybrid grounding 

  4. Floating grounding

In this article, we will focus on single-point and multipoint grounding. 

Single-Point and Multipoint Grounding

There are advantages and disadvantages to both single-point and multipoint grounding. Let’s first take a closer look at single-point grounding before we move on to a discussion of multipoint grounding.

Single-Point Grounding

In single-point grounding, isolated circuits or subsystems in a circuit board are connected to a physical point in the circuit—a single-point ground. This point acts as the grounding reference to all the subsystems or components in the circuit. This single ground point is considered to be at zero potential with respect to the whole circuit. Single-point grounding is the preferred type of grounding for low-frequency analog circuits

Single-point grounding can be further classified into two categories—series single-point grounding and parallel single-point grounding. 

Series Single-Point Grounding

In series single-point grounding, circuits are connected to a single point. Series single-point grounding is a simple method; suitable for when the grounding wires connecting the modules to the ground point are short. Otherwise, problems may arise due to the impedances of the connecting wires. 

There are certain things to watch out for with series single-point grounding. 

Things to Watch Out For

Why Is This important?

No series single-point grounding for high power circuits.

The finite impedance causes voltage drops between the circuit and the ground point. 

Random placement of different power level circuits is not a good idea when using series single-point grounding.

The placement of the sensitive circuit closer to the power input and away from the low power circuits better supports the purpose of series single-point grinding.

If there is a power level difference between the circuits, series single-point grounding is not suitable.

The large return current from high power circuits affects low-power circuits.

Parallel Single-Point Grounding

In this type of single-point grounding, the ground current of each module and ground impedance are the only factors affecting the grounding system at low frequency. Parallel single-point grounding is suitable for resolving low-impedance interference issues in circuits working at low frequencies.

At high frequency, parallel single-point grounding is affected by ground impedance, ground inductance, and capacitance between grounding wires. Mutual coupling between the grounding wires exists, and this coupling effect can cause issues in the circuit. The individual lines from modules to the single ground point increase the grounding wire length and ground impedance, which causes further complications affecting circuit operation. 

Multipoint Grounding

Multipoint grounding connects each circuit or module in the nearest ground-plane with the shortest length of the wire. The ground plane is the common-low impedance equipotential plane where all the multiple grounding wires terminate.

Multipoint grounding is suitable for high-frequency circuits and high-speed digital circuits. Multipoint grounding establishes multiple parallel paths between two points and the ground plane. This grounding scheme simplifies circuit construction in complex equipment.

As you can see, single-point and multipoint grounding both have their advantages and disadvantages. Choosing which to use in a circuit depends on the frequency specifications of your circuit. Luckily, Cadence’s software assists with circuit design as well as grounding schemes.   

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