Master of Engineering Balram Sahu - Embedded Sensing ...

Chapter 4Flip-Flop CharacterizationIn theory any logic system can be built using universal cells (NAND or NOR) or usingAND, OR and NOT gates but as the complexity of circuit design grows, it becomesimpractical to design circuits by hand. Therefore, the use of automatic synthesis toolshas become mandatory. The use of synthesis and PNR tools requires the provision ofcell library. So the first step of the design is to develop such a library, or to acquire one.There are two most common properties that a layout library must posses.The first requirement is the functional completeness. Synopsys’ Design Analyzersynthesis tool require the library to contain, at minimum, six different types of cells,namely:• One type of tristate cell.• Either NOR and NAND gates or AND and OR gates.• Inverter• D flip-flop with asynchronous set and reset.• D latch with asynchronous set and reset.The second requirement pertains to the shape and sizes of cells. The shape and sizesof standard cells must be very regular. This also applies to the geometries inside the cellsparticularly those on metal layers. These requirements are intended to ensure that PNRtools would be able to lay down the routing tracks without being obstructed by metalgeometries.17