Connected Circuit

This rule checks for the validity of circuit usage and whether the routing length and clearance from driver pins are within the specified distance.

When a trace has noise or EMI problem or it is very weak against ESD, designer may not have any other routing option to resolve the problem. In such case, special purpose circuits, such as pull-up/pull-down, filter circuits, ESD prevention circuits and fan-out circuits, may be used. If those circuits are used in design, this DFE rule checks whether they are used properly. In many cases, those circuits should be placed near active drivers with controlled signal lengths. For example, damping resistor circuits should be placed closest to driver pins.
  • Item: Input item name.
  • Net: Select a net group that needs a rectification filter circuit.
  • Filter Circuit: Select a rectification filter circuit.
  • Circuit AND/OR: If filter components are more than one, use this option.
    • OR: If one of the filter components is located within specific distance, it passes.
    • AND: Check if all selected filter components are located within specific distance.
  • Start Comp: Select a component from which the circuit starts.
  • Check Value: Assign distance value to which a rectification filter component must be located from the staring component. This rule check reports the following messages:
    • No Filter: when there is no rectification component in target nets.
    • No Start Comp: when there is no starting component in target nets.
    • Distance Fail: when there is a rectification component in target net, but it violates the distance rule. In this case, it also reports the reference distance and measured distance.

Rectification circuit (or filter circuit) is a circuit to pass necessary frequencies but blocks or eliminates unnecessary frequencies. The purpose of using this filter is to get stability of signal. So, for important signal, it is necessary to check whether those nets have proper types of filter. In fact, it is very difficult to improper usage of filters without an aid of tools like PollEx DFE.

There are four major types of rectification filters: low pass, high pass, band pass, and band elimination (band stop) filters.

Figure 1.
In general, Low Pass filter is used to pass low frequencies and reduce high frequencies as noise filter. When filters are used, the designer should be cautious about their locations in signal trace.

Figure 2.

Locations of p1, p2 and p3 are decided depending on the circuit characteristics and environment. Between p1 and p3, it is necessary to define maximum distance.