Transcript Tuesday
Physical Implementation 1) Manufactured Integrated Circuit (IC) Technologies 2) Programmable IC Technology 3) Other Technologies Manufactured IC Technologies If you took a pencil and made the smallest dot that you could on a sheet of paper, that dot’s area would hold many thousands of transistors on a modern silicon chip. How can chip makers create such tiny transistors? The key lies in photography. Chip makers lay a special chemical onto the chip, special because the chemical changes when exposed to light. Chip makers then shine light through a lens that focuses the light down to extremely small regions on the chip - similar to how a microscope’s lens lets us see tiny things by focusing light, but in reverse. The chemical in the small illuminated region changes, and then a solvent washes away the chemical but some regions stay because of the light that changed that region. Those remaining regions form parts of transistors. Repeating this process over and over again, with different chemicals at different steps, results not only in transistors, but also wires connecting the transistors, and insulators preventing crossing wires from touching. Custom Integrated Circuits Only 10% of digital designs are implemented as custom ICs. • Calculators • Watches • Pentium Application Specific Integrated Circuits (ASICs) 1) Gate Array • Cheaper • Faster fabrication • Slower performance • Bigger size • More power consumption 2) Standard Cells • More optimized • Slower fabrication Programmable IC Technology Field Programmable Gate Arrays (FPGAs) To implement the desired circuit we program an FPGA chip (download a series of bits into chip’s memories). • Circuit is ready in minutes • 10 times slower • 20 times bigger Lookup Tables A memory can implement a combinatorial circuit. A memory used to implement combinatorial circuit is known as a lookup table. Example 7.3: Implementing the seatbelt warning light with a lookup table Partitioning a Circuit among Lookup Tables We need 2N word memory for a function with N variables. 3-input 2-output lookup tables work best for most circuits. Programmable Interconnects (Switch Matrices) The point of FPGA is that the entire chip is pre-fabricated – including the wires. Programmable interconnects (switch matrices) allow us to program the connections among lookup tables. Example 7.6: 24 decoder on an FPGA with a switch matrix Configurable Logic Block How many bits to download?