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Booth Muxes Interleaved with Carry Save Adders Array

IP.com Disclosure Number: IPCOM000115920D
Original Publication Date: 1995-Jul-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 68K

Publishing Venue

IBM

Related People

Klim, P: AUTHOR [+3]

Abstract

The method disclosed is a combining of the functions of an array of multiplexors and Carry Save Adders (CSAs) to produce an interleaved single array that performs the same logic function while achieving area reduction and reduced delay derived from the shorter wire lengths between the muxes and the CSA elements.

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Booth Muxes Interleaved with Carry Save Adders Array

      The method disclosed is a combining of the functions of an
array of multiplexors and Carry Save Adders (CSAs) to produce an
interleaved single array that performs the same logic function while
achieving area reduction and reduced delay derived from the shorter
wire lengths between the muxes and the CSA elements.

      The above method has been used in the design of the 630
multiplier both in the integer and floating point units.  The array
consists of booth multiplexors and 9 to 2 compressors.  Each of the 9
to 2 compressor consists of nine booth muxes and seven CSAs.  Three
sets of three booth muxes drive the three first level CSAs.  Each
booth mux receives two data inputs and five control signals.  The
fifth control signal is needed (drive zero) because dual rail dynamic
CMOS is utilized and the circuit is required to evaluate every cycle.
With the generation of nine partial products every cycle, 45 control
signals were needed plus an additional 3 signals for precharging the
three sets of booth muxes.  Due to the performance and area
constraints of the 630 the height of the array had to be minimized.
The prior method is shown in Fig. 1 where the booth muxes are located
as a separate array above the CSA array.  To connect the 48 control
lines to the booth muxes and with the need to use wider metal to
reduce delay and coupling between lines the wiring area became a
critical contributor to the height...