Reference Designer

This article is third in the series of Signal Integrity. In first article of the series, I discussed Integrity of Point to Point Signal . In second article of the series, I discussed Tips for Cross talk Reduction .

Tips for Power Supply Noise Reduction

1. Design a stack up that keeps power and ground planes together.
2. Keep the separation between power and ground plane as small as possible.
3. Design a stack up that uses more power and ground planes.
4. Use bigger vias to connect decoupling capacitors to power and ground layers. Your system should have at least two types of vias, smaller vias for high speed signals and larger vias for power and ground connections.
5. Use wider traces to connect decoupling capacitors to power and ground planes.
6. Keep vias connecting power and ground ends of a decoupling capacitor as close as possible.
7. For larger capacitors use multiple vias to connect power and ground signals.
8. Use ceramic decoupling capacitor that has wider metal contact to lower the ESL (Effective Series Inductance). For example, a 0612 Capacitor will have lower ESL than 1206 even with same physical size.
9. Place decoupling capacitors as close to the IC power pins as possible.
10. If you are using multiple vias to connect a large capacitor to a power plane, keep them apart. Similarly, keep the multiple vias connecting the ground end of a large capacitor far.
11. Prefer a package with short leads. In DDR, for example if a choice is available use BGA package over SSOP package.
12. Use large number of decoupling capacitor to reduce total effective series inductance.
13. Use smaller size decoupling capacitor. Prefer 0402 over 0603 or 0805.
14. Place power supply regulator IC close to the place where it will be used to minimize.

Vikas Shukla is currently working as Senior Design Engineer at BL Healthcare. He has degree in Computer Science and Engineering from IT-BHU, Varanasi, India. Mr. Shukla has over 15 years of experience in design of microprocessor-based systems. His expertise includes signal integrity, architecture and design of remote patient monitoring systems. The views expressed are his own.

This article is pre-edited excerpts from his forthcoming book “Signal Integrity for PCB Designers”.

Signal Integrity Add new tag, cross talk, si, tips

In my previous article I talked about the signal Integrity tips for point to point signals. This article extends the tips for Cross talk reduction in a PCB.

Tips for Cross talk Reduction

1. Give preference to stripline over microstrip when routing critical signals sensitive to cross talk.
2. Reduce the separation between the signal and ground layers as far as possible while still achieving the required impedance.
3. Space out the critical high speed traces as much as possible. A minimum spacing of twice the signal width is a good number.
4. Pay special attention to high speed clock signals. Keep other traces away from clock signals.
5. Use guard traces if the very high immunity to noise is required.
6. If guard trace is used, use vias to connect the guard trace to ground.
7. For traces running in parallel, the cross talk level increases with the increase in length of parallelism. The far end crosstalk or FEXT saturates after a certain length ( depending upon the rise time of the signal) and the cross talk does not increase further. There is no gain in trying to minimize the length of parallelism beyond the critical length.
8. Make sure traces in adjacent layers run perpendicular to each other.
9. Add thicker soldermask on the top and bottom layer. This will decrease far end cross talk.
10. Use lower dielectric constant material. The lower dielectric constant reduces the separation between the signal and the return plane, thereby reducing the crosstalk.
11. Use a design with lower characteristic impedance.

By Vikas Shukla

Vikas Shukla is currently working as Senior Design Engineer at BL Healthcare. He has degree in Computer Science and Engineering from IT-BHU, Varanasi, India. Mr. Shukla has over 15 years of experience in design of microprocessor-based systems. His expertise includes signal integrity, architecture and design of remote patient monitoring systems. The views expressed are his own.

This article is pre-edited excerpts from his forthcoming book “Signal Integrity for PCB Designers”.

Uncategorized cross talk, si, Signal Integrity