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High Performance Self-Reset CMOS TXOR and CXOR Circuits

IP.com Disclosure Number: IPCOM000113116D
Original Publication Date: 1994-Jul-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 37K

Publishing Venue

IBM

Related People

Shah, KB: AUTHOR

Abstract

Figs. 1 and 2 show high performance six transistor Self-Reset CMOS - TXOR and CXOR circuits. These circuits are used in the high speed cache memory of a comparator. The TXOR and CXOR circuits compare two dual rail inputs and generate a single rail output. A special self-reset feature of these circuits is that the TXOR and CXOR outputs do not change state until valid data arrives at the inputs.

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High Performance Self-Reset CMOS TXOR and CXOR Circuits

      Figs. 1 and 2 show high performance six transistor Self-Reset
CMOS - TXOR and CXOR circuits.  These circuits are used in the high
speed cache memory of a comparator.  The TXOR and CXOR circuits
compare two dual rail inputs and generate a single rail output.  A
special self-reset feature of these circuits is that the TXOR and
CXOR outputs do not change state until valid data arrives at the
inputs.

      The initial state of the TXOR circuit in Fig. 1 is as follows:
A and Anot are low (0 state), B and Bnot are high (1 state), node $1
is high, and the output of inverter I1 is low.  A and Anot are
complementary inputs;  therefore, if the input data is high, then A
goes from an initial low to a high, and Anot remain low.  B and Bnot
also are complementary inputs.

      Input signals A and Anot also select which transistor (N1 or
N2) is turned on, thereby selecting which signal (B or Bnot) appears
at the node $1.  For instance, if A is high (Anot is low), then
transistor N1 is turned on and the value of B appears at node $1;
the inverse of node $1 appears at the TXOR output.  Thus, if B is
low, then node $1 is pulled low, and TXOR output is high.
Conversely, if A is low (Anot is high), then transistor N2 is turned
on, and the value Bnot appears at node $1.  The operation of the CXOR
circuit in Fig. 2 is similar to the operation of the TXOR circuit
described above.