MOSFET Look-Ahead Bit Incrementer/Decrementer
Original Publication Date: 1985-Jul-01
Included in the Prior Art Database: 2005-Feb-18
A modified look-ahead circuit is featured which may be programmed to increment or decrement by one without complicating the chip wiring and without increasing the power dissipation of the circuit. To convert a basic look-ahead bit incrementer into a selective incrementer or decrementer by one circuit (see figure), the following changes were made: 1.) One Mode (increment/decrement) input line was added. 2.) Two sets of enhancement MOSFET pass transistors (1-6) for multiplexing complemented or non-complemented data to the inputs of the NOR gates. The complemented input data was already available in the basic look-ahead incrementer to create the Exclusive OR function. 3.) An inverter stage 7 in the Mode line was added to complement the mode input state and keep the two sets of pass transistors mutually exclusive.