Testing and Simulations Part II
In Part I, we looked at testing methodology for backplanes. In this feature, we will review simulation methodology.
Simulation for custom backplanes is becoming a more important issue in design and development. Bustronic has submitted a bid for simulations for the PICMG 2.17 subcommittee for StarFabric. We’ve also been working with the connector companies for information on their simulation studies. The scope of the work is to optimize the signal pinouts and study the effects of interference of nearby and adjacent signals. In today’s switched fabric backplanes, one can perform 622Mbps LVDS (Low Voltage Diffferential Signaling) simulations in 2mm HM connectors or non-standard connectors.
First, we create an HSPICE (Simulation Program with Integrated Circuit Emphasis) model based on the connector and PWB model and layout. Then, in terminating certain pins and leaving others open, we perform crosstalk analysis from adjacent and non-adjacent pins. This includes grounded pins and AC grounded pins, etc. The simulation is done for various signal assignments and we look for the problems and restraints. From there, we determine the optimum pinout for the signals. In backplanes using LVDS, simulations for both multi-point and single-point are often required. (Single point - a single point experiment is a relatively simple procedure that produces a single result, or a single set of output data.
Multipoint - an analysis [single-point] sweep is performed for each value in an outer loop [multi-point] sweep.)
In analyzing waveforms, cross-probing allows probing a net in the schematic window and viewing its signal. Cross-probing is supported for signals generated by transient, DC, or AC analysis. The cross-probing feature also allows pins to be probed for branch currents.
Many of the connector companies have simulated eye diagrams of their connectors in standard FR-4 PWB material. The backplane trace lengths and trace spacing can also be studied for optimum performance. There are also a lot of areas that we won’t go into in this newsletter issue -- like system simulation, daughter card effects etc. But, feel free to contact us more questions on simulation or other issues.
Melissa Heckman
Electrical Engineer
Melissa has over fourteen years of experience as an electrical
engineer, and has been with Bustronic for two years. She earned
her electrical engineering degree from Cal Poly San Luis Obispo
in 1987.
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