Power integrity (PI)

Power Integrality, referred to as PI, is to confirm whether the voltage and current of Power source and destination meet the requirements. Power integrity remains one of the biggest challenges in high-speed PCB design.

The level of power integrity includes chip level, chip packaging level, circuit board level and system level. Among them, the power integrity at the circuit board level should meet the following three requirements:

1. Make the voltage ripple at the chip pin smaller than the specification (for example, the error between voltage and 1V is less than +/ -50mv);

2. Control ground rebound (also known as synchronous switching noise SSN and synchronous switching output SSO);

3, reduce electromagnetic interference (EMI) and maintain electromagnetic compatibility (EMC) : power distribution network (PDN) is the largest conductor on the circuit board, so it is also the easiest antenna to transmit and receive noise.

Power integrity problem

The power supply integrity problem is mainly caused by the unreasonable design of decoupling capacitor, the serious influence of circuit, the bad segmentation of multiple power supply/ground plane, the unreasonable design of formation and the uneven current. Through power integrity simulation, these problems were found, and then the power integrity problems were solved by the following methods:

 (1) by adjusting the width of PCB lamination line and the thickness of dielectric layer to meet the requirements of characteristic impedance, adjusting the lamination structure to meet the principle of short backflow path of signal line, adjusting the power supply/ground plane segmentation, avoiding the phenomenon of important signal line span segmentation;

 (2) power impedance analysis was conducted for the power supply used on the PCB, and the capacitor was added to control the power supply below the target impedance;

 (3) in the part with high current density, adjust the position of the device to make the current pass through a wider path.

Power integrity analysis

In power integrity analysis, the main simulation types include dc voltage drop analysis, decoupling analysis and noise analysis. Dc voltage drop analysis includes analysis of complex wiring and plane shapes on the PCB and can be used to determine how much voltage will be lost due to the resistance of the copper.

Displays current density and temperature graphs of “hot spots” in PI/ thermal co-simulation

Decoupling analysis typically drives changes in the value, type, and number of capacitors used in the PDN. Therefore, it is necessary to include parasitic inductance and resistance of the capacitor model.

The type of noise analysis may vary. They can include noise from IC power pins that propagate around the circuit board and can be controlled by decoupling capacitors. Through noise analysis, it is possible to investigate how the noise is coupled from one hole to another, and it is possible to analyze the synchronous switching noise.