Automated Design for Micromachining

# Donut

## Introduction

This parameterized cell draws a donut. However, it provides two advantages over the simple shape provided by Virtuoso. First, it calculates the number of sides necessary to meet the manufacturing tolerance. Second, it allows specification of a start and stop angle, allowing designers to draw partial donuts.

The behaviour of this parameterized cell is close related to that of the circle parameterized cell. Please refer to that documentation as well.

## Theory

### Tolerance

Please refer to the same section in the documentation for the circle parameterized cell.

## Parameters

Any parameter may be modified, if necessary, to meet design rules. Typically, this involves increasing parameters that specify distances, so that minimum line width and minimum line spacing rules will not be violated. This has been extended to the convention of specifying a zero for some parameters to obtain an instance of the minimum size.

In addition to the parameters listed below, several technology parameters also influence the implementation of parameterized cells. This data must be present in the technology library.

Table 1: Parameters for the 'donut' parameterized cell.
Name Description Range Units
layer This must be one of the drawing layers in the technology, and specifies the layer onto which the circle will be drawn. dwg layers -
inner radius This parameter specifies the inner radius of the donut. While a value of zero can be specified, the radius will be increased, if necessary, to ensure that the circle does not violate any design rules. [0,∞) um
outer radius This parameter specifies the outer radius of the donut. While a value of zero can be specified, the radius will be increased, if necessary, to ensure that the circle does not violate any design rules. [inner radius,∞) um
angle This parameters controls what portion of the donut's arc will be drawn. With, obviously, 360° specifying a full circle. (0,360] degrees
rotation Cadence does not natively support rotations by increments other than 90°. To overcome this limitation, a rotation of up to 45° can be specified. Combined with the reflections about X and Y axes, any arc in any position can be drawn. [0,45) degrees
tolerance This parameter specifies the upper limit on which the polygon generated to approximate the inside and outisde arc (or portion thereof) can deviate from a true circle. While a value of zero can be specified, if the tolerance is less than half of the technology's manufacturing grid, it will be increased before the donut will be approximated. [0,inner radius] um

## References

The documentation for this parameterized cell does not contain any references.