The integrity of an interconnect can be described in terms of the signal, or in terms of the power. Both are important, but signal integrity specifications usually get all the headlines.
Signal integrity (SI) examines the fidelity of the signal’s shape and amplitude. Typical issues are: the overall energy transmitted, high frequency responses, crosstalk and reflections.
Power integrity (PI) examines the fidelity of the power and ground distribution. Typical issues are: voltage stability, power loss, ground bounce and the frequency limits of pulsed power demands.
Why is PI important ?
All electronic devices – no matter how fast or slow, or how big or small – need clean and predictable power to work properly. If voltage levels are uncertain or if they fluctuate rapidly, then the device results will be uncertain.
How does an interconnect impact PI ?
Power integrity is influenced by the classical interconnect parameters of: Capacitance (C), Resistance (R), and Inductance (I).
- Capacitance along an interconnect path will affect the stability of the voltage.
- Resistance along the interconnect path will cause a drop in voltage and a loss of power.
- Inductance along the interconnect path will impede the flow of current.
What’s important ?
The distributed capacitance of a power pin in a connector or socket is not a major factor in power integrity analysis. If capacitance is needed, discrete capacitors can be placed along the interconnect path – from the power supply, to the PCB, and even the device package.
Resistance and inductance are the important specifications.
Resistance causes a voltage drop according to Ohm’s Law (v = i * r). It also results in a loss of power (p = i2 * r) and the creation of heat.
This is of particular significance when a device operates at low voltages, or processes analog signals. It is also significant when a large number of interconnections are concentrated in a small area.
Resistance is determined by these factors:
Comparison of resistance values and current ratings.
Inductance restricts the flow of current – especially during peak demands – as a result of an interconnect’s physical shape or a nearby magnetic field.
Inductance is determined by these factors:
Comparison of inductance values and lengths:
What makes a PariPoser® elastomer good for PI ?
PariPoser® anisotropic elastomer has magnetically aligned particles of silver plated nickel that are set into a sheet of silicone. Current passes down the particle columns, but not between neighboring columns. For each contact position, there are about 10 particle columns.