Advancements in Digital IC Technology
The continuous evolution of digital IC technology is characterized by the decreasing size of transistor features. As submicron technology progresses, the integration density of digital ICs increases, leading to faster speeds. However, this progress comes with higher power consumption and a decrease in core supply voltage, a trend expected to continue in the future.
Understanding Power Integrity (PI) and Power Distribution Network (PDN)
PDN encompasses the entire power system that provides power to active circuits on a PCB. It includes connections from the Voltage Regulator Module (VRM) to the IC die and pads, facilitating power delivery and return current. Components like VRM, decoupling capacitors, traces, and PCB planes contribute to the PDN structure.
In high-speed PCBs, adjacent copper layers serve as power and ground, forming a power/ground pair or power bus. Multiple ICs in dense PCBs share common power/ground pairs. The PDN impedance, influenced by current spectrum, causes voltage fluctuations due to switching currents, known as Simultaneous Switching Noise (SSN).
Key Characteristics of a Well-Designed PDN System
- Ensures a stable power supply voltage to the load.
- Prevents transmission of AC noise from the load.
- Maintains zero AC impedance between power and ground.
Basic Requirements for Practical PDN Systems
- Maintains a constant voltage between chip solder pads.
- Minimizes ground bounce effects.
- Avoids electromagnetic interference (EMI) issues.
Estimating Target Impedance of PDN
The Importance of Power Delivery Network (PDN) Impedance in PCB Design
The impedance of the Power Delivery Network (PDN) plays a crucial role in managing the transient power supply current spectrum of digital Integrated Circuits (ICs). In modern designs, multiple power supply voltages are common, each with varying power ripple indices, operating conditions, and transient power current spectra for different ICs.
It is essential to tailor the target impedance of the PDN to each IC’s specific requirements to ensure optimal performance. Maintaining the impedance below the target value across the power supply current spectrum is key in PDN design. Exceeding the target impedance can result in excessive power supply ripple, while significantly lower impedance may lead to unnecessary design costs.
The Future of Power Integrity (PI) and PDN Impedance
Looking ahead, Power Integrity (PI) will only grow in significance for digital products. The trend is towards decreasing the target impedance of the PDN to meet evolving technological demands. PI is intricately linked to the PDN and must align with the unique needs of each product.
Designing an effective PDN involves ensuring that the impedance consistently remains below the target value throughout the transient power current spectrum. This balance is critical for optimal performance and cost-efficiency in PCB design.
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