Virtuoso AMS Environment User Guide

Working with Schematic Designs

netSet and is a legal net name, its value is used as the connecting net rather than the default net name specified in the expression.

The netSet property can be placed on any instance and it affects all net expression labels with matching property names at all levels below that instance unless overridden by another netSet property on a lower-level instance.

Net and Pin Properties

The AMS environment supports the following properties. The last three are in addition to those listed in “Properties” on page 610.

Virtuoso AMS Environment User Guide

Working with Schematic Designs

supplySensitivity For information, see “groundSensitivity and supplySensitivity Properties” on page 173

groundSensitivity and supplySensitivity Properties

The groundSensitivity and supplySensitivity properties provide a way to make a connect module sensitive to supplies in the module to which the connect module is connected.

Typically the port of the connected module is a digital port. It is possible to make a connect module sensitive to supplies in an analog port but making the connect module sensitive to supplies in the connected digital port is much more likely to produce the behavior that you expect. This is so because:

■When the connect module converts analog signals to digital values, the decision to output a one or a zero depends on the relationship between the analog signal and a threshold value. The threshold value is determined by the supply values in the component that includes the connected digital port.

■When the connect module converts digital values to analog signals, the connect module needs to determine what voltage to produce for each digital input value. Again, that voltage depends on the supplies in the component that includes the connected digital port

Overview of the Sensitivity Properties

The groundSensitivity and supplySensitivity properties, which are added to a port or pin definition, have the following syntax.

sensitivity_properties ::=

(* [ integer groundSensitivity = "sig1_sensitive_to" ; ]

[ integer supplySensitivity = "sig2_sensitive_to" ; ] *)

sig1_sensitive_to, sig2sensitive_to

Names of signals, typically global signals, to which a connect module is made sensitive.

When the groundSensitivity property is included as part of a signal declaration in the connect module, the declared signal takes on, by default, the value of sig1_sensitive_to. When the groundSensitivity property is included as part of a signal declaration in an ordinary module, the sig1_sensitive_to value in that module overrides the sig1_sensitive_to value specified in the connect module. The supplySensitivity property works similarly.

Virtuoso AMS Environment User Guide

Working with Schematic Designs

For example, the connect module might be defined as follows.

connectmodule l_to_e(dval, aval);

...

electrical (* integer groundSensitivity = "global_pwr.pow1" ; *) gnd ;

...

endmodule

This connect module is connected to the digital port d in an ordinary module that is defined as follows.

module sample(d);

output (* integer groundSensitivity = "global_pwr.pow5" ; *) d ;

...

endmodule

In this example, gnd is defined in the connect module as taking on, by default, the value of global_pwr.pow1, but that value is overridden by the value global_pwr.pow5 specified in the module sample when the connect module is inserted across the digital port d. To generalize, if the groundSensitivity property is not used in the ordinary module, the connect module uses the default value specified on thegroundSensitivity property in the connect module.

Basic Principles for Using the Sensitivity Properties

Some basic principles will help you use the groundSensitivity and supplySensitivity properties correctly.

■Connect modules are always inserted between a digital port and an analog net. When you use the groundSensitivity and supplySensitivity properties, you make the connect module sensitive to the signals on the digital port. That is true whatever the direction of the port might be.

■There are two steps involved in establishing ground or supply sensitivity: inserting the necessary properties in the connect module; and adding the corresponding properties to the connected digital port. If the connected digital port is part of a schematic, you define the properties on the connected pin in the schematic. If the connected digital port is defined in a text module, you add the properties to the port definition in the module.

■The default value associated with the groundSensitivity and supplySensitivity properties must be the name of a signal, not the name of a property.

■You must use detailed discipline resolution or the sensitivity properties have no effect.

Virtuoso AMS Environment User Guide

Working with Schematic Designs

Example: Using the Sensitivity Properties in a Chain of Buffers

Assume that you have the following schematic containing three buffers. Buffers ba1 and ba3 are instances of a module that is implemented as an analog block with analog input and output pins. Buffer bd2 is implemented as a digital block, with logic input and output pins.

During elaboration, connect modules are inserted across net n1 and the digital input port of buffer bd2, and across the digital output port of buffer bd2 and net n2.

Assume that the string of buffers is designed to run at 5.0 volts. The connect module must then be written to work at that voltage. For example, an A2D connect module with hardcoded thresholds set for 5.0 volts might look like this.

‘include "disciplines.vams" connectmodule elect2logic(aVal, dVal);

output dVal; input aVal; logic dVal; electrical aVal;

endmodule

But assume now that the string of buffers can run at either 3.0 volts or 5.0 volts, depending on the supplies that are provided. To make the connect module sensitive to the supplies, you use the groundSensitivity and supplySensitivity properties, and rewrite the always statement so that the threshold is calculated from the supply and ground values.

‘include "disciplines.vams"

connectmodule elect2logic(aVal, dVal); output dVal;

input aVal; logic dVal; electrical aVal;