The analysis and design of power supply system (PDS) is becoming more and more important in the field of high-speed circuit design, especially in computer, semiconductor, communication, network and consumer electronics industries. With the inevitable further proportional reduction of VLSI technology, the supply voltage of integrated circuits will continue to decrease. As more and more manufacturers switch from 130nm technology to 90nm technology, it can be predicted that the supply voltage will drop to 1.2V or even lower, while the current will increase significantly. From the point of view of DC IR voltage drop to AC dynamic voltage fluctuation control, because the allowable noise range is getting smaller and smaller, this development trend has brought great challenges to the design of power supply system.
Usually, in AC analysis, the input impedance between power supply and ground is an important observation to measure the characteristics of power supply system. The determination of this observation value evolved into the calculation of IR voltage drop in DC analysis. In the analysis of DC or AC, the factors that affect the characteristics of the power supply system are: the layering of PCB, the shape of the power board plane, the layout of components, the distribution of vias and pins, etc.
The concept of input impedance between power sources and ground can be applied to the simulation and analysis of the above factors. For example, a very wide application of input impedance of power supply is to evaluate the placement of decoupling capacitors on board. With a certain number of decoupling capacitors placed on the board, the unique resonance of the circuit board itself can be suppressed, thus reducing the 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, the system design engineer must always consider how to choose the system layout of decoupling capacitors economically and effectively.
The power supply system in high-speed circuit system can usually be divided into three physical subsystems: chip, integrated circuit package structure and PCB. The power grid on the chip consists of several metal layers alternately placed. Each metal layer consists of metal strips in X or Y direction to form a power grid or a ground grid, and vias connect the metal strips in different layers.
For some high-performance chips, many decoupling units are integrated regardless of the power supply of the core or IO. The integrated circuit package structure, like a reduced PCB, has several layers of complex power supply or ground plane. On the upper surface of the package structure, the installation position of decoupling capacitor is usually reserved. PCB usually contains a continuous large-area power supply and ground plane, as well as some discrete decoupling capacitor elements, large and small, and a power rectifier module (VRM). Bonding wires, C4 bumps and solder balls connect the chip, package and PCB together. The whole power supply system should ensure that each integrated circuit device is provided with a stable voltage within the normal range. However, the switching current and the parasitic high-frequency effects in those power supply systems will always introduce voltage noise.
