Layout_Examples

213 top layout view of an mos transistor showing gate

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Unformatted text preview: sion area. Before deciding the size, a designer needs to know at which frequency the circuit must operate. For example, a circuit designer might be given a list of requirements that says “The target multiplier must be running at 50MHz and take 0.1mA from a 3.3V supply.” This is the starting point where the numbers are called the circuit specifications, or specs. With detailed information about a particular process, the specs can determine the necessary device sizes. Many different circuit techniques can be used to design a component such as a multiplier. A designer chooses a circuit topology among them that will give the required performance. Then, the designer calculates the basic capabilities of the circuit and verifies that the circuit meets the specs. The way to verify IC design assumptions is to build the circuit and run it. The designer runs the design through a computer program called a simulator. The simulation program indicates what the circuit does, how much current it consumes, the frequency response, etc. These circuit simulation programs are commonly called Simulation Program for Integrated Circuits Emphasis 6 (SPICE). The original SPICE was developed by the University of California at Berkeley in the 1970’s. Running a simulation is cheaper and faster than building a chip. In order for SPICE to accurately predict the complex behaviors of a circuit, a mathematical representation of the circuit elements is needed. This is called a model. The model accurately reflects the physics of the device and its electrical and physical characters. The SPICE simulation results show how the circuit performs with the given device sizes and values. Since the input values in the simulation deck can be adjusted easily, the simulator allows designers to sweep the input data, and they can tune the device sizes and values to optimize the design. Some layout tips are found in the following subsections [SNT, BTT, CLN]. Long and Thin Transistors Many processes have a design rule specifying...
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This document was uploaded on 01/14/2014.

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