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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.
- Spring '13