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Load Sharing Among SELECT Signals

IP.com Disclosure Number: IPCOM000035755D
Original Publication Date: 1989-Aug-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Weinberger, A: AUTHOR

Abstract

DCS (Differential Current Switch) logic is comprised of the primitive function SELECT from which the simpler functions, XOR, AND and OR, are derived.

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Load Sharing Among SELECT Signals

DCS (Differential Current Switch) logic is comprised of the primitive function SELECT from which the simpler functions, XOR, AND and OR, are derived.

A large SELECT function is implemented in 2 or more stages of smaller SELECT functions that are available as single gates. For example, Let F be a one-of-16 SELECT function as follows:

(Image Omitted)

where A, B, C, and D comprise a 4-bit select code and DO through D15 comprise the 16 data signals of which one is selected.

The first stage, for example, uses signals C and D to select one of 4 data signals from each of 4 groups of data signals. The second stage then uses signals A and B to select one of the 4 groups. In equation form

(Image Omitted)

Note that signals C and D are in the critical path of the implied logic and each of their decoded values (C.D, C.D, C.D, and C.D) sees 4 loads.

To reduce the load on C and D, the equation for F is changed so as to allow all four select signals, A through D, to participate in the first stage logic, as follows:

(Image Omitted)

The advantages of load sharing become more obvious when implementing a still larger SELECT function. For example, a 64-way SELECT function using a 6- bit code (A, B, C, D, E and F) may use 4 of the 6 code bits (say C, D, E and F) to select data signal from each of 4 sets of 16 data signals in the first two stages if 4-wat SELECT gates. An equation similar to the example above is used. The remaining 2 code bits, A and B...