Time and Distance

Setup and hold time is useful for chip designers and simulation engineers. As PCB designers, we need to finally measure the things in terms of the length of the trace that travel on the PCB.

The electric signals are electromagnetic wave and their speed of propagation depends upon the dielectric constant of the material surrounding it. The Formula for the speed of propagation is .
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Timing Relationship between Signals

If you have already designed some high speed PCBs or if you have been involved in some way in high speed PCB design, you must have come across design rules that require the difference in the length of the PCB trace to be within a specified limit.
These rules are often results of the relation between the clock and data signal timing. There is a timing window in which the data must arrive at the rising edge or falling edge of the clock. If the data arrives too early and goes away or if it arrives too late it is of no use.
Let us take some time to understand the concept of the setup and hold time and see how we can ensure its proper implementation at the PCB level.

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Tom and Bob

As part of the book, I will be covering the conversation between Tom and Bob. Tom is a novice PCB designer willing to learn about Signal Integrity. He does not think much before asking a question. Some times he poses intelligent question. Sometime he irritates Bob with his question. But Bob has patience.
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Periodic Waves and Fourier Transform

A perfectly sinusoidal clock or signal seldom happens in real world. We encounter square waves, sawtooth waves, deteriorated square waves. Cycle after cycle, these waves repeat the same pattern. In other words, the instantaneous value of these waves is same after some fixed amount of period. These waveforms are called periodic waves. The fixed amount of time after which the signal repeats is called period of the wave.
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Knee Frequency

n analyzing high speed digital signals, many factors depend upon the frequency of the signal. This includes, for example, the value of the impedance of the capacitance, signal path loss. Knee frequency is an estimate of the highest frequency content of the signal. It depends upon the rise time of the signal. If the rise time is smaller, the highest frequency content will have higher frequency. If t denotes the 10% to 90% rise time of a signal, then an estimate for the highest frequency content of the signal or the knee frequency is given by
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PCB Design for High Speed

As a PCB Designer you need to alter your habits a little bit, if you want your board to work for high speed.

As soon as you receive the board from the designer you need to stop and spend some time on the signal integrity aspect of the design. This may mean that you will have to spend some extra time on your already long list of tasks of creating footprints, maintaining library, doing placement, doing routing, maintaining revisions, generating gerber files and creating documentation.
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Electromagnetic Radiation

The PCB traces and ICs carrying the high speed signal can be source of radiation. A high edge rate causes more chances of signal radiation. Traces that are not adequately terminated lead to more reflection and higher emission. The clock oscillators are major sources of radiation. The radiation pattern observed in a spectrum analyzer shows frequencies that are usually a multiple or harmonics of clock oscillators used in design.
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