PCB Tech - PCB power supply system design

The analysis and design of power supply system (PDS) is becoming more and more important in the field of high-speed PCB design, especially in the computer, semiconductor, communications, network and consumer electronics industries. With the inevitable further scaling down of VLSI technology, the power supply voltage of integrated circuits will continue to decrease. As more and more manufacturers switch from 130nm technology to 90nm technology, it is foreseeable that the power supply voltage will drop to 1.2V or even lower, while the current will also increase significantly. From the DC IR voltage drop to the AC dynamic voltage fluctuation control, as the allowable noise range is getting smaller and smaller, this development trend has brought a huge challenge to the design of the power supply system.

1. Usually in AC analysis, the input impedance between power and ground is an important observation used to measure the characteristics of the power supply system. The determination of this observation has evolved into the calculation of IR voltage drop in DC analysis. Whether in the analysis of DC or AC, the factors that affect the characteristics of the power supply system are: PCB layering, the shape of the power board layer plane, the layout of components, the distribution of vias and pins, and so on.

2. The concept of input impedance between power and ground can be used in the simulation and analysis of the above factors. For example, a very wide application of power ground input impedance is to evaluate the placement of decoupling capacitors on the board. With a certain number of decoupling capacitors placed on the board, the unique resonance of the circuit board itself can be suppressed, thereby reducing the generation of noise, and also reducing the edge radiation of the circuit board to alleviate the electromagnetic compatibility problem. In order to improve the reliability of the power supply system and degrade the manufacturing cost of the system, system design engineers must often consider how to economically and effectively select the system layout of decoupling capacitors.

The power supply system in the high-speed circuit system can usually be divided into three physical subsystems: chip, integrated circuit packaging structure and PCB. The power grid on the chip is composed of several metal layers alternately placed. Each metal layer is composed of thin metal strips in the X or Y direction to form a power or ground grid, and via holes connect the thin metal strips of different layers.

3. The PCB factory integrates many decoupling units for some high-performance chips, no matter the core or IO power supply. The integrated circuit packaging structure, like a reduced PCB, has several layers of power or ground planes with complex shapes. On the upper surface of the package structure, there is usually a place to install the decoupling capacitor. The PCB layout usually contains a continuous power and ground plane with a larger area, as well as some large and small discrete decoupling capacitor components, and a power rectifier module (VRM). Bonding wires, C4 bumps, and solder balls connect the chip, package, and PCB together. The entire power supply system must ensure that each integrated circuit device provides a stable voltage within the normal range. However, switching currents and parasitic high-frequency effects in power supply systems always introduce voltage noise.