High-Speed PDN Design and Power Integrity Analysis Discussed by Steve Sandler
In the realm of electronic system design, calculating target impedance for Power Distribution Network (PDN) designs is a crucial task that requires a deep understanding of the frequency-dependent nature of impedance. This article provides a guide on how to approach this challenge, using both designer tools and rule-of-thumb methods.
## Designer Tools
Designer tools, such as simulation software offered by companies like Ansys, play a significant role in accurately modeling and simulating PDN impedances. These tools consider the physical layout of the PCB, including trace geometry, material properties, and capacitive effects, allowing for precise calculations and analyses of PDN impedance across various frequencies.
1. **Simulation Software**: Start by creating a detailed model of your PCB layout, including all components and their connections. Use software like Ansys to simulate the electrical behavior of your PDN, computing impedance at different frequencies. Tools like these can provide detailed reports on impedance, helping you identify potential issues and optimize your design.
2. **Impedance Calculators**: Utilize impedance calculators specifically designed for PCB design. These tools calculate impedance based on trace width, material properties, and other factors. Enter parameters like trace width, dielectric height, and dielectric constant to obtain calculated impedance values.
## Rule of Thumb Methods
For simpler estimations or initial design phases, rule-of-thumb methods can be useful:
1. **Frequency-Dependent Targets**: Target impedance should be less than 1 mΩ at DC (0 Hz) to ensure reliable power delivery. At high frequencies, such as 10 GHz, aim for impedance under 100 mΩ to maintain signal integrity.
2. **Series Resistance and Inductance**: Consider the series resistance and inductance of vias and traces, as these significantly affect impedance at higher frequencies. Use approximations or simplified models to estimate these contributions to overall impedance.
3. **Decoupling Capacitors**: Place multiple decoupling capacitors to maintain low impedance across different frequency ranges. Ensure that capacitors are placed close to the load and that their values are appropriately chosen for the frequency range of interest.
## General Guidelines
- **Layout and Geometry**: Uniform trace geometry and consistent return paths are crucial for maintaining controlled impedance. - **Material Properties**: Accurate control over material properties, such as dielectric constants, is essential for meeting impedance targets. - **Component Placement**: Strategically place components like capacitors and voltage regulators to minimize impedance variations.
By combining these methods, designers can effectively calculate and manage target impedance for PDN designs, ensuring reliable power delivery and signal integrity in electronic systems.
Steve Sandler, the founder of Picotest, a company that specializes in power integrity solutions, is an expert in the design, measurement, modeling, and simulation of power, PDN, and lumped element RF circuits. Picotest is also showcasing a new set of adapters for oscilloscopes that allow for measuring two-port PDN and impedance in the oscilloscope.
Wide-bandgap is the latest trend in the power integrity world, transforming the world of electronics in a big way. The Picotest Bode 100 Vector Network Analyzer can measure frequency response, power supply rejection ratio, control loop gain, and can be reconfigured to measure S-parameters with the frequency response analyzer. Dielectric absorption, the cause of transmission line losses, can be reduced by using lower loss materials and making the layers thinner and the traces narrower.
In conclusion, understanding and managing target impedance for PDN designs is a vital aspect of electronic system design. By employing a combination of designer tools and rule-of-thumb methods, designers can ensure reliable power delivery and signal integrity, leading to the creation of high-performing electronic systems.
- Controlled Impedance Calculations: When creating your PCB layout model, utilize impedance calculators to calculate impedance based on trace width, material properties, and other factors, which will help you to maintain controlled impedance in your PDN design.
- Technology Advancements: Steve Sandler, the founder of Picotest, leverages technology advancements in power integrity solutions, such as the Picotest Bode 100 Vector Network Analyzer, to measure frequency response, power supply rejection ratio, and control loop gain, enabling designers to reduce dielectric absorption and improve overall performance in electronic systems.
