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VHDL-AMS Analog Variables: Quantities

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Quantities are purely analog variables and can be defined in one of three ways. Free quantities are simply analog variables that do not have a relationship with a conserved energy system. Branch quantities have a direct relationship between one or more analog terminals, and finally source quantities are used to define special source functions (such as AC sources or Noise sources).

For example, to define a simple analog variable called x, which is a voltage but not related directly to an electrical connection (terminal), then the following VHDL could be used.

1 quantity x : voltage;

On the other hand, a branch between two electrical pins has a through variable (current) and an across variable (voltage) and this requires a branch quantity so that the complete description can be solved simultaneously. For example, the complete quantity declaration for the voltage (v) and current (i) of a component between two pins (p and m) could be defined as:

1 quantity v across i through p to m;

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