PCB Power Design for High Speed DSP System
This article addresses several issues that should be noted in the design of PCB board reliability in high-speed DSP systems.
When designing PCB board with high-speed DSP system, the power design issues are the first one to consider. In power supply design, the following methods are commonly used to solve signal integrity problems.
I.Consider the decoupling of power and ground
With the increase of DSP operating frequency, DSP and other IC components tend to be miniaturized and the packaging is more compact. Usually circuit design consider using the multilayer board, the proposed power and ground can use a special layer, and for a variety of power sources, such as DSP's I/O supply voltage and the core supply voltage is different, you can use two different power planes. If you think the processing cost of multilayer board is high, you can place power supply which has more wire or is relatively critical on a special layer, other power and signal lines can be put as the wiring, but be careful that the width of the line should be sufficient.
Regardless of whether the printed circuit board has a specific ground and power planes, a reasonable and well-distributed capacitor must be placed between the power and ground. In order to save space, you can reduce the number of vias, and use more chip capacitors. Chip capacitors can be placed on the back of the PCB board that is the soldered surface, use a wide wire to connect chip capacitors and through-holes, and connect power and ground by using the through-hole.
II.Consider the wiring rules for power distribution
a.Separate analog and digital power planes
High-speed, high-precision analog components are sensitive to digital signals. For example, the amplifier amplifies the switching noise and brings it closer to the pulsed signal, so the power planes are typically required to be separate from the analog and digital sections of the board.
b.Isolate sensitive signals
Some sensitive signals (such as high-frequency clocks) are particularly sensitive to noise, thus they need to take high-level isolation measures. High-frequency clock (above 20MHz, or the flip time is below 5ns) must have ground escort with at least 10mil clock line width and at least 20mil escort ground line width. Besides, high-frequency signal line protection ground must have a good contact with ground layer under the help of through hole. The clock transmitting side must be connected in series with a 22Ω ~ 220Ω damping resistor to avoid the interference caused by signal noise.