BACK END HARDWARE ENGINEER
Logical Gate Level
At the Logical Gate Level the design is represented by a netlist that uses only cells from a small number of single-bit cells, such as basic logic gates (AND, OR, NOT, XOR, etc.) and registers (usually D-Type Flip-flops). A number of netlist formats exists that can be used on this level such as the Electronic Design Interchange Format (EDIF), but for ease of simulation often a HDL netlist is used. The latter is a HDL file (Verilog or VHDL) that only uses the most basic language constructs for instantiation and connecting of cells.
Physical Gate Level
On the Physical Gate Level only gates are used that are physically available on the target architecture. In some cases this may only be NAND, NOR and NOT gates as well as D-Type registers. In the case of an FPGA-based design the Physical Gate Level representation is a netlist of LUTs with optional output registers, as these are the basic building blocks of FPGA logic cells.
Switch Level
A Switch Level representation of a circuit is a netlist utilizing single transistors as cells. Switch Level modeling is possible in Verilog and VHDL, but is seldom used in modern designs, as in modern digital ASIC or FPGA flows the physical gates are considered the atomic build blocks of the logic circuit.
⦁ Planning Switch Level Hardware
A Floor-Planner of an Integrated Circuit (IC) is a schematic representation of tentative placement of its major functional blocks. In modern electronic design process floor-plans are created during the floor-planning design stage, an early stage in the hierarchical approach to Integrated Circuit design. Depending on the design methodology being followed, the actual definition of a floor-plan may differ.
⦁ Placing Switch Level Hardware
A Standard Cell Placer takes a given synthesized circuit netlist together with a technology library and produces a valid placement layout. The layout is optimized according to the aforementioned objectives and ready for cell resizing and buffering, a step essential for timing and signal integrity satisfaction. Physical design flow are iterated a number of times until design closure is achieved.
⦁ Timing Switch Level Hardware
A Standard Cell Timing-Analizer is a simulation method of computing the expected timing of a digital circuit without requiring a simulation of the full circuit. High-performance integrated circuits have traditionally been characterized by the clock frequency at which they operate. Measuring the ability of a circuit to operate at the specified speed requires an ability to measure, during the design process, its delay at numerous steps.
⦁ Routing Switch Level Hardware
A Standard Cell Router takes pre-existing polygons consisting of pins on cells, and pre-existing wiring called pre-routes. Each of these polygons are associated with a net. The primary task of the router is to create geometries such that all terminals assigned to the same net are connected, no terminals assigned to different nets are connected, and all design rules are obeyed.
⦁ Simulating Switch Level Hardware
A Standard Cell Simulator treats transistors as ideal switches. Extracted capacitance and lumped resistance values are used to make the switch a little bit more realistic than the ideal, using the RC time constants to predict the relative timing of events. This simulator represents a circuit in terms of its exact transistor structure but describes the electrical behavior in a highly idealized way.
⦁ Verifying Switch Level Hardware
A Standard Cell Verifier compares netlists, a process known as LVS (Layout vs. Schematic). This step ensures that the geometry that has been laid out matches the expected circuit. The greatest need for LVS is in large analog or mixed-signal circuits that cannot be simulated in reasonable time. LVS can be done faster than simulation, and provides feedback that makes it easier to find errors.
⦁ Checking Switch Level Hardware
A Standard Cell Checker is a geometric constraint imposed on Printed Circuit Board (PCB) and Integrated Circuit (IC) designers to ensure their designs function properly, reliably, and can be produced with acceptable yield. Design Rules for production are developed by hardware engineers based on the capability of their processes to realize design intent. Design Rule Checking (DRC) is used to ensure that designers do not violate design rules.
⦁ Printing Switch Level Hardware
A Standard Cell Editor allows to print a set of standard cells. The standard cell methodology is an abstraction, whereby a low-level VLSI layout is encapsulated into a logical representation. A standard cell is a group of transistor and interconnect structures that provides a boolean logic function (AND, OR, XOR, XNOR, inverters) or a storage function (flipflop or latch).
References: http://opencircuitdesign.com/ http://www.clifford.at/yosys/
