ANALOG BEHAVIORAL MODELING WITH THE VERILOG-A LANGUAGE- P4: Verilog-A is a new hardware design language (HDL) for analog circuit and systems design. Since the mid-eighties, Verilog HDL has been used extensively in the design and verification of digital systems. However, there have been no analogous high-level languages available for analog and mixed-signal circuits and systems. | Analog Events The statement following the event expression is executed whenever the event expression triggers. Analog event detection in the Verilog-A language is non-blocking meaning that the execution of the statement is skipped unless the analog event has occurred. This non-blocking behavior is a general characteristic of any statement within the analog statement. The event expression consists of one or more monitored events separated by the or operator. The or-ing of any number of events can be expressed such that the occurrence of any one of the events trigger the execution of the event statement that follows it as @ analog_event_1 or analog_event_2 statement Cross Event Analog Operator The cross event analog operator is used for generating a monitored analog event to detect threshold crossings in analog signals. FIGURE cross analog operator and its graphical representation. The cross function generates events when the expression argument crosses zero in the specified direction. cross controls the timestep to accurately resolve the crossing within a time resolution of timetol and value resolution of valuetol. Both timetol and valuetol are optional. If the direction argument dir is 0 or not specified then the event and timestep control occur on both positive and negative crossings of the signal. If the direction indicator is 1 -1 then the event and timestep control only occurs on positive negative transitions of the signal. These cases are illustrated graphically in Figure . For any other transitions of the signal the cross function does not generate an event. Behavioral Descriptions 75 Please purchase PDF Split-Merge on to remove this watermark Behavioral Descriptions FIGURE Illustration of the different specifications of the direction parameter for the cross analog operator. The use of timetol is relevant for rapidly changing signals. If the cross analog operator is used to delineate regions of behavior in the model then .
