Signal Integrity, Part 2
In Part 1 of his signal integrity series, Columnist Barry Olney examined how advanced IC fabrication techniques have created havoc with signal quality, and radiated emissions. Part 2 covers the effects of crosstalk, timing, and skew on signal quality.
Signal Integrity, Part 1 of 3
As system performance increases, the PCB designer’s challenges become more complex. The impact of lower core voltages, high frequencies, and faster edge rates has forced us into the high-speed digital domain. But in reality, these issues can be overcome by experience and good design techniques. If you don’t currently have the experience, then listen-up.
Material Selection for Digital Design
In his latest column, Barry Olney looks at what types of materials are commonly used for digital design, and how to select an adequate material to minimize costs. He advises, "Of course, selecting the best possible material will not hurt, but it may blow out the costs."
Beyond Design: Concurrent Design
Concurrent design is the practice of developing products in which the different stages run simultaneously rather than consecutively. It decreases product development time and also time-to-market, leading to improved productivity and reduced costs. The practice is a relatively new process strategy and although the initial implementation can be challenging, the competitive advantage means it is beneficial in the long term.
Surface Finishes for High-Speed PCBs
PCB surface finishes vary in type, price, availability, shelf life, assembly process, and reliability. While each treatment has its own merits, electroless nickel immersion gold (ENIG) finish has traditionally been the best fine pitch (flat) surface and lead-free option for SMT boards over recent years. But, unfortunately, nickel is a poor conductor with only one third the conductivity of copper.
Beyond Design: Transmission Line - From Barbed Wire to High-speed Interconnect
Contrary to common belief, the transmission line does not carry the signal itself but rather guides electromagnetic energy from one point to another. It is the movement of the electromagnetic field or energy, not voltage or current that transfers the signal. The voltage and current exist in the conductor, but only as a consequence of the field being present as it moves past.
Mythbusting: There are No One-way Trips!
One of the greatest myths in PCB design is that we only have to route signal traces from pin-to-pin to make a complete connection. And, that ensuring these traces have matched delay is the only timing issue we need to consider. However, current is not a one way trip--it must complete the circuit back to the source to provide the round-trip current loop.
Matched Length Does Not Always Equal Matched Delay
In previous columns, Columnist Barry Olney has discussed matched length routing and how matched length does not necessarily mean matched delay. But, all design rules, specified by chip manufacturers regarding high-speed routing, specify matched length--not matched delay. In this month's column he takes a look at the actual differences between the two.
Beat the Traffic Jam - Effective Routing of Multiple Loads
In a previous column, Barry Olney discussed various termination strategies and concluded that a series terminator is best for high-speed transmission lines. But, what if there are a number of loads--how should these transmission lines be routed? For perfect transfer of energy and to eliminate reflections, the impedance of the source must equal the impedance of the trace(s) to the load.
PDN Planning and Capacitor Selection, Part 2
In Part 1 of this column, Barry Olney looked closely at how to choose the right capacitor to lower the AC impedance of the power distribution network (PDN) at a particular frequency. This month he continues from there looking at the one-capacitor-value-per-decade and optimized value approaches.