a gate-level netlist in the target technology of the chip. Floorplanning: The RTL of the chip is assigned to gross regions of the chip, input/output (I/O) pins are assigned and large objects (arrays, cores, etc.) are placed. Placement: The gates in the netlist are assigned to nonoverlapping locations on the die area. Logic/placement refinement: Iterative logical and placement transformations to close performance and power constraints. Clock insertion: Clock signal wiring is (commonly, clock trees) introduced into the design. Routing: The wires that connect the gates in the netlist are added. Postwiring optimization: Performance (timing closure), noise (signal integrity), and yield (Design for manufacturability) violations are removed. Design for manufacturability: The design is modified, where possible, to make it as easy and efficient as possible to produce. This is achieved by adding extra vias or adding dummy metal/diffusion/poly layers wherever possible while complying to the design rules set by the foundry. Final checking: Since errors are expensive, time-consuming and hard to spot, extensive error checking is the rule, making sure the mapping to logic was done correctly, and checking that the manufacturing rules were followed faithfully. Chip finishing with Tapeout and mask generation: the design data is turned into photomasks in mask data preparation. Analog design Before the advent of the microprocessor and software based design tools, analog ICs were designed using hand calculations and process kit parts. These ICs were low complexity circuits, for example, op-amps, usually involving no more than ten transistors and few connections. An iterative trial-and-error process and "overengineering" of device size was often necessary to achieve a manufacturable IC. Reuse of proven designs allowed progressively more complicated ICs to be built upon prior knowledge. When inexpensive computer processing became available in the 1970s, computer programs were written to simulate circuit designs with greater accuracy than practical by hand calculation. The first circuit simulator for analog ICs was called SPICE (Simulation Program with Integrated Circuits Emphasis). Computerized circuit simulation tools enable greater IC design complexity than hand calculations can achieve, making the design of analog ASICs practical. As many functional constraints must be considered in analog design, manual design is still widespread today. As a result, modern design flows for analog circuits are characterized by two different design styles – top-down and bottom-up. The top-down design style makes use of optimization-based tools similar to conventional digital flows. Bottom-up procedures re-use “expert knowledge” with the result of solutions