Circuit reliability challenges for the automotive industry

There is another important reliability concern in the automotive area—how to handle negative voltages that occur in automotive applications—that is closely tied to the processing of reverse current issues in high-voltage electrical rule checking. This reliability concern can also be addressed with an advanced reliability verification tool.

This type of checking has two sides: schematic and layout. Let’s start with the schematic side. Designers must specify which ports on the schematic are subjected to negative voltage. They can then use the voltage propagation functionality to propagate these negative voltages across devices, based on user-defined propagation criteria for the different device types. Propagating the negative voltages helps designers identify all the nets in that design that may become negative (our example uses the Calibre PERC static approach). The user-defined propagation criteria may include a voltage drop definition to be taken into consideration while propagating through the devices, which is also supported by the voltage propagation functionality. Including this criteria leads to the negative voltages decreasing in absolute value when they are propagated through devices. The propagation should be terminated if the internal net has positive voltage. The user can now identify all devices attached to these nets that have propagated negative voltage, consider them the injectors, and export them to proceed with the next step on the layout side.

Using Calibre PERC functionality, designers can perform a cross-reference between the schematic and the layout to capture the injectors’ locations on the layout. Then, moving to the layout, designers can run the needed geometrical operations (using a tool like Calibre DRC or Calibre PERC LDL DRC) to search for the affected sensors’ locations within a certain distance from injectors, and define a severity for this case for every injector and all its associated sensors. The severity assignment is based on:

• the designer’s review of the distance between every injector and sensor
• what the sensor is connected to
• what other layout elements are between the injector and the sensor

Using this designer-defined severity to determine priority, the design team decides what to fix in the layout to address the reliability concern. All the violations from both schematic and layout side can be debugged using a results viewing environment, where the designer can highlight the results and analyze them.

Using circuit reliability verification and DRC technology together, users now have an easy, automated, and efficient flow to perform checking for both negative voltages and reverse current issues in automotive applications. This automated flow from a concept perspective is similar to what was demonstrated before in Figures 1 and 2. Of course, the input voltages, the propagation criteria, and some of the rules are different from those applied to the voltage drop-dependent metal spacing rules described earlier.