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Browse Prior Art Database

Pre-Decoded Gray Code Counter

IP.com Disclosure Number: IPCOM000104826D
Original Publication Date: 1993-Jun-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 2 page(s) / 50K

Publishing Venue

IBM

Related People

Hiltebeitel, N: AUTHOR [+2]

Abstract

A method is described for using a Gray pre-decoder at a counter output to minimize the number of simultaneously switching signals that are distributed throughout an integrated circuit. Reducing the number of simultaneously switching signals reduces peak and average current and power on the chip.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Pre-Decoded Gray Code Counter

      A method is described for using a Gray pre-decoder at a counter
output to minimize the number of simultaneously switching signals
that are distributed throughout an integrated circuit.  Reducing the
number of simultaneously switching signals reduces peak and average
current and power on the chip.

      In conventional N-bit binary coded counters, the maximum number
of bits that can switch simultaneously is N. The average number of
bits that can switch simultaneously varies with N, but can be as high
as two.  Pre-decoding schemes are used to reduce the number of
simultaneously switching bits, thereby reducing both peak and average
input current and input power.  A code that is particularly
advantageous is the Gray code in which only one bit is allowed to
switch at a time.  With Gray coding, both the maximum and average
number of bits that switch in any one cycle is one.  Gray coding
reduces peak current and power to as little as 1/N of the values
obtained with conventional binary coding.  Average current and power
are reduced to as little as 50% of conventional values.

      A first example of 1 of 4 pre-decoding that does not use Gray
code is shown in Table 1.  A second example that uses Gray code is
shown in Table 2.  All bit combinations are not shown, but the Gray
characteristic of only one bit (Z line) change per count is evident.

     TABLE 1: NON-GRAY CODE                  TABLE 2: GRAY CODE

Z(12-15)  Z(8-11)  Z(4-7)  Z(0-3)     Z(12-15)  Z(8-11)  Z(4-7)
Z(0-3)
   12        8        4       0          12        8        4       0
   12        8        4       1          12        8        4       1
   12        8        4       2          12        8        4       2
   12        8        4       3          12        8        4       3
   12        8        5       0          12        8        5       3
   12        8        5   ...