Fast Parity Tree
Original Publication Date: 1989-Dec-01
Included in the Prior Art Database: 2005-Jan-29
A fast parity tree is shown which can improve a parity generator delay performance by about 80% while maintaining the same macro size over a previous design. (Image Omitted)
Fast Parity Tree
A fast parity tree is shown which can improve a parity generator delay performance by about 80% while maintaining the same macro size over a previous design.
A parity generator and checker are required in a microprocessor to either create the parity bit to be stored or check the integrity of the data read. When the parity generator is connected in series in one of the critical paths of a processor, the delay of the circuit is reflected directly on processor performance. The existing parity generator is designed as a chain of Exclusive-OR (XOR) circuits. The XOR is designed as a 2-way NOR followed by 2 + 1 AND-OR-Invert circuit. The total number of delay stages is 7 for a total delay of 5.6 ns. A new parity generator, where the XOR and XNOR are generated at each level of the tree, is utilized to reduce the total number of logic delays. The new circuit results in an 80% improvement in delay with no impact on macro density.
The new parity generator uses an XOR circuit that requires true and complement inputs. Figs. 1 and 2 show the different implementations of the XOR and XNOR circuit that can be utilized for the parity tree. Both implementations have the same circuit configuration for XOR and XNOR, only some input connections are switched. Fig. 3 shows the logic diagram of the parity generator with the total number of logic delays reduced to 5. In this parity tree, the XOR and XNOR functions are generated in parallel...