Optimized High Speed Digital Tutorial

Ssabsdurr

Informations

• Publié par: Dihom
• Nombre de lectures: 27
• Langue: English

Extrait

High Speed Digital Interconnects and Signal Integrity

1

0

Digital Signal Integrity

This is what we would like to have:

1

0

This is more like what we get in real life:

This would be considered to be a “clean” signal.

In real life, it is not always 1,0,1,0…

Signal Aberrations

We are trying to create a Square Wave, but Mother Nature just won t let us do it! ’

It is Physically Impossible to create a perfect Square Wave!

Logic Levels Possible Bit Error

The Signal Voltage must make into the “End Zone”

within the allotted period of time.

Pulse Risetime

Risetime is the most important factor in determining Bandwidth requirements.

Differential Signaling

•

•

•

Immunity from Ground Noise

Immunity to Electromagnetic Interference

Works with low Voltages, saves Power

Differential Mode

Common Mode

Twinax / Quadrax

Field Patterns

Twinax Electric Field

Twinax Magnetic Field

Eye Pattern

The Eye Pattern is simply a bunch of pulses, both positive and negative, chopped up and overlaid upon each other.

It is an easy way to evaluate the Signal Integrity of Thousands of pulses at a glance.

The shape of each pulse is affected by the whether the previous pulse was a 1 or 0.

This is why we need to use a Pseudo Random Bit Stream (PRBS) to simulate an actual data stream.

Eye Pattern Mask

High Speed Digital & Signal Integrity

• •

•

•

What makes High Speed Digital different than old fashion digital? The High Frequency content of the Digital Signal requires that High Frequency Design Techniques be taken into account in order to preserve the Signal Integrity. Understanding High Frequency Design Techniques requires understanding the basics of Transmission Line Theory. First, we need to understand the High Frequency content of the Digital Signal…

Frequency Content of the Digital Signal

Mother Nature can’t create Square Waves, she can only create Sine Waves.

Waves of any other shape are Composed of Overlapping Sine Waves.

Square Waves are composed of a Superposition of Odd Harmonic Sine Waves.