VHDL-AMS Hardware Description Language:Mixed-Signal Design

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Mixed-Signal Design

A mixed-signal system is composed of digital and analog parts each of which has its own constructs, data formats, and timing models. What is important in a mixed-signal system is the interaction of these two parts to exchange the required data at the correct time.

To utilize continuous values in the digital part of a model, these values must be sampled and scaled to the appropriate values at discrete time instances. Sampling can be performed by utilizing a process statement that is sensitive to the sampling event. The 'above attribute can be used to trigger the sampling event.

After sampling continuous values at discrete-time instances, these values must be converted into appropriate values using type conversions supported by VHDL-AMS. Figure 91.15 shows an example for the use of 'above attribute.

In contrast, the signals deļ¬ned in the digital part of a system can be used by the simultaneous statements of the analog part using VHDL-AMS type conversions. To consider the discontinuity that appears on the resulted analog parameters, break statements as well as 'ramp, and 'slew attributes can be used. Figure 91.16 shows an example for the use of 'ramp attribute.

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