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LVDS PCB Layout Guidelines

Published Date
Author Cadence PCB Solutions

Key Takeaways

  • LVDS PCB layout guidelines can be used for optimizing system performance by ensuring reliable signal integrity and reducing the chances of noise interference. 

  • Careful differential pair routing, impedance control,  grounding, and noise reduction techniques are key factors for performance optimization. 

  • Advanced simulation and analysis tools can help designers optimize the design process through the validation of the LVDS PCB layout guidelines. 

LVDS PCB layout guidelines

When designing a PCB layout for LVDS (Low-Voltage Differential Signaling) signals, designers may need to follow some crucial guidelines to achieve optimal signal integrity and a reduced level of noise interference. LVDS, with its differential signaling technology, transmits data as a voltage difference between the two lines instead of a single voltage level. The benefit of this approach includes reduced EMI (electromagnetic interference) and low power consumption. 

This article will focus on how to leverage these benefits by developing comprehensive LVDS PCB layout guidelines that cover key aspects such as routing, impedance control, and grounding.

Differential Pair Routing

LVDS signals rely on differential signaling, where the data is transmitted as a voltage difference between two signals. Proper routing techniques ensure signal balance, minimize skew, and reduce electromagnetic interference. 

LVDS PCB Layout Guidelines for Differential Pairs

  • Trace Symmetry: The positive and negative signals of the differential pairs should be routed closely together to maintain signal balance. Symmetrical routing ensures that traces of the differential pair are equal in terms of length, impedance, and spacing throughout the routing path. The symmetry should also consider factors like reference planes and alignment to help reduce the risk of coupling, noise, and signal degradation. By achieving trace symmetry in differential pair routing, it is possible to ensure reliable data transmission while avoiding timing issues. 
  • Trace Length Matching: Matching the lengths of the positive and negative traces helps preserve signal timing and minimize skew. Skew can lead to timing errors and signal degradation. To ensure length matching, designers can use length tuning or trace meandering techniques. 
  • Crosstalk Prevention: LVDS signals are susceptible to crosstalk from nearby traces. To reduce interference, it is important to maintain adequate spacing between the differential pair and the neighboring signal traces. The larger the spacing, the better the isolation. However, the positive and negative traces of the differential pair must be placed closer and parallel to each other. This is important for maintaining the signal integrity and minimizing the crosstalk and EMI. 

Considerations for Impedance Control

LVDS PCB layout guidelines should focus on proper impedance control in order to minimize signal reflections and ensure optimal transmission. The table below details some considerations to make for impedance control.  

PCB Layout Guidelines and Considerations: Impedance Control

Considerations

Description

Characteristic Impedance
  • Calculate the required trace width and spacing to achieve the desired characteristics impedance based on PCB stack-up and dielectric properties.
  • Use impedance calculation tools for specific dimensional values based on your design requirements.

Differential Pair Impedance Matching
  • Ensure the positive and negative traces of the differential pairs have matched impedance.
  • The characteristic impedance of both traces should be the same to maintain balanced signaling.

PCB Stack-Up
  • Select the appropriate dielectric materials and layer configuration to achieve the desired impedance.
  • Consider the dielectric constant and thicknesses of the PCB layer when designing the trace dimensions.

Considerations for Grounding and Noise Reduction

LVDS PCB layout guidelines should highlight proper grounding techniques to minimize noise interference and ensure a stable reference for signal transmission. Here are a few factors to consider: 

Power Management IC (PMIC) Design Solutions

Considerations

Description

Solid Ground Plane
  • Include a solid ground plane beneath the LVDS traces for a low-impedance return path for the signals.
  • Ensure that the ground plane is continuous and uninterrupted to minimize noise coupling.

Power and Ground Decoupling
  • Place decoupling capacitors near the LVDS transceiver ICs for clean and stable power supplies.
  • Use low inductance and low ESR (Equivalent Series Resistance) capacitors for effective decoupling.
  • Connect the capacitor ground terminals to the ground plane with short traces.

Power Integrity and Noise
  • Incorporate electrostatic discharge protection components such as TVS (Transient Voltage Suppression) diodes or dedicated electrostatic discharge protection devices near the LVDS connectors or at vulnerable points.

Maximize System Performance With LVDS PCB Layout Guidelines 

LVDS PCB layout guidelines aim to ensure optimal signal integrity and minimize noise interference by considering factors like impedance control, differential pair routing, grounding, etc. Implementation of these guidelines can help designers maximize the performance of the LVDS-based system across a wide range of applications. This can be facilitated by tools such as Allegro X, which helps designers create and customize PCB stack-ups, route differential pairs, and define controlled impedance traces. With the simulation and analysis capabilities of Allegro X, designers can validate the layout through signal integrity simulation, impedance matching, and crosstalk analysis to resolve potential issues in the design process. 

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