[sv-dc] Examples of how back-annotated parasitics would be modeled without resolutions functions tied to nets

I've received enough calls and emails that my previous communications haven't been clear. Here's are three examples of back annotation methods that Scott and I went through, and hopefully it will clear up some confusion. In each example, the only language features needed are resolution functions tied to a type, and user-defined types on ports. Feel free to call or email me if there are any questions.

In modeling parasitic resistance between three devices, a distributed parasitic resistance provided by the drives will solve the problem very accurately. For example, consider this Thevenin driver module and interconnect:

module driver #(parameter rParasitic=0.0) (Thev_t w1);

  initial w1 <= {internalDriverVoltage, inernalDriverResistance+rParasitic);

endmodule

module BackAnnotatedNetlist ();

  parameter rParasitic1 = 1.2e3;

 parameter rParasitic2 = 1.5e3;

  parameter rParasitic2 = 1.8e3;

  Thev_t interconnectNet;

  driver #(rParasitic1) inst1(interconnectNet);

  driver #(rParasitic2) inst2(interconnectNet);

  driver #(rParasitic3) inst3(interconnectNet);

endmodule

This is a trivial case and the accuracy degrades for more interconnect branches. For more devices, the branches of the wires get complicated. In this case, actual discrete resistances and/or capacitors can be used. There's probably a limit to how many discrete devices one would be able to use for a net, but that's difficult to determine without a lot of investigation. Here is an example of such an netlist in which three driver devices and two resistors are connected in a Daisy chain (one resistance between driver 1 and driver 2, and a second resistor between driver 2 and driver 3). The resistors are similar to the discrete resistor example I provided in VHDL. Other wiring parasitic topologies are implemented in similar ways.

module BackAnnotatedNetlist ();

  parameter rParasitic1 = 1.2e3;

  parameter rParasitic2 = 1.5e3;

  Thev_t interconnectBranch1, interconnectBranch2, interconnectBranch3;

  driver #(0) inst1(interconnectBranch1);

  resistor #(rParasitic1) branch1(interconnectBranch1, interconnectBranch2);

  driver #(0) inst2(interconnectBranch2);

  resistor #(rParasitc2) branch2(interconnectBranch2, interconnectBranch3);

  driver #(0) inst3(interconnectBranch3);

endmodule

Finally, to solve Achim's desire to have a module for the interconnect, we simply instantiate one specific to an interconnect. This interconnect module can also take in heterogeneous driver types. However, it can not always be implemented in a hierarchically accurate netlist. It must be a flat netlist. This may be a problem in some cases. Maybe someone can comment if this is a concern.

module BackAnnotatedNetlist ();

  parameter rParasitic1 = 1.2e3;

  parameter rParasitic2 = 1.5e3;

  Thev_t interconnectBranch1, interconnectBranch2, interconnectBranch3;

  driver #(0) inst1(interconnectBranch1);

  driver #(0) inst2(interconnectBranch2);

  driver #(0) inst3(interconnectBranch3);

  interconnectModel123 #(rParasitic1, rParasitic2) interconnect(interconnectBranch1, interconnectBranch2, interconnectBranch3);

endmodule

Kindest Regards,
Jim Lear
Cirrus Logic
(512) 851-4612
(512) 293-7248 (mobile)

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