Summary

NetBom provides a set of utilities that allows users to trace all nets in a given netlist and graphically display the traces in a browser.

Net tracing behavior is governed by a collection of configuration settings (CSets) that allow the user to have control over certain aspects of how the traces are executed and displayed.

Our graphical net trace is not bound by physical or logical pages making it especially useful for checking nets or segments of a design that span more than one page.

All net traces stop at ground and power nets, and they stop at a configurable set of part types (connectors/ic by default). They also can optionally stop when reaching nets and/or parts of a particular size (node count).

Example

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Above is an example of a typical small trace. The base net is MAX8668_ENOUT, the trace has been configured to stop at all connectors so we see U1, U5, and U6 showing up as components that have not been traced through. NetBom has determined that P3R3V is a power net, so it stops when reaching that, and AGND was determined to be a ground net so it stops there as well.

Net Trace Types

There are three main types of traces that NetBom performs. The different types will render slightly differently, will be traced differently, and are configured by different CSets.

1. Power Trace

2. Diff Pair Trace

3. Regular Trace

Power Trace

Power traces are traces on nets that NetBom has identified as a power rail or a ground net.

These traces, because of their inherent size, are limited in scope compared to the other trace types.

Power traces will contain the rail that is being traced in addition to all the parts on the rail. The trace will also make an exception when it reaches a part on a rail that is connected to a single net that only has net-stop components on it. In this case, it will include that net and all its components in the trace. The power trace can also be configured to trace through low-ohm resistors as well, which it does by default.

This configuration allows for viewing what each power rail is connected to (particularly the grounded capacitors) without the additional parts and nets that would be produced by a normal trace.

Power Trace Configurations

When tracing a power rail, we allow the user to optionally trace through low-ohm resistors until it reached a capacitor. The ohm limit is configurable in the CSet POWER_RAIL_RESISTOR_OHM_LIMIT. The default is 10.

The capacitor part types are configurable with the CSet POWER_RAIL_CAP_PART_TYPES. The default part types are CAPACITOR and POLARIZED_CAP. When the power trace encounters a part with any one of these part types it will stop the trace and add the part to the list of capacitors on the rail.

Example Power Trace

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This cropped power trace has P3R3V as its base net. It stops the trace at the first two resistors R23 and R16 before it reaches a part that is attached to a net with only net-stop components, J1 and U6, so the net SGD_PWRGD and its parts are added to the trace before it continues. The POWER_RAIL_RESISTOR_OHM_LIMIT is set at the default of 10 Ohms, so when the trace reaches the next two resistors, R32 and R11, it traces through them and grabs the capacitors on the opposite end which are displayed in the power rail summary for this rail (not displayed in picture).

Diff Pair Trace

Diff pair traces are similar to regular traces, except that they are always rendered with their opposite pair. NetBom does its best to render the diff pair traces in a mirrored fashion with connected nets clearly indicated.

Example Diff Pair Trace

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In this example, the diff pair W0_CK_P and its opposite net W0_CK_N are rendered on top of each other, with the connected net BOL_CK_T_W0 linking the two together.

Regular Net Trace

Finally, the rest of the traces that NetBom produces are considered regular net traces.

These traces can be configured with the following CSets: