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Circuit Description

A demonstration of a few complex logic gates, namely the OR-AND-INVERT and OR-AND-INVERT gates.

Click the input switches to toggle the corresponding input value between 0 and 1, and watch the resulting behaviour. You can also use shift+click to toggle the input value between the states 0, 1, Z (tri-state, not driven) and X (undefined).

The names of these gates are derived from their AND-OR-INVERT and OR-AND-INVERT structure and the number of inputs of the first level gates. To give another example, an OAI222 gate (not shown in the applet) is equivalent to three two-input OR gates that drive a three-input NAND gate.

Complex gates are often used in CMOS VLSI chip design because they can be realized very efficiently, based on clever combinations of series- and parallel-connected transistors. For example, the AOI33 gate can be built using just 12 transistors, while the corresponding discrete realization would require 4 transistors for the NOR gate, and 8 transistors for each AND3 gate for a total of 20 transistors - almost twice as expensive and twice as slow.

Visit our CMOS technology applet page for a detailed (switch-level) demonstration of a complex gate.

To explore the circuit, just click the corresponding switches, or type the following keys:

• a,s,d (AOI21)
• f,g,h (OAI21)
• 1,2,3,4,5,6 (AOI33)
• y,u,i,o,p (OAI32)