Electronic digital logic circuitry – Function of and – or – nand – nor – or not – Field-effect transistor
Patent
1997-02-24
1998-02-17
Westin, Edward P.
Electronic digital logic circuitry
Function of and, or, nand, nor, or not
Field-effect transistor
326108, H03K 190948
Patent
active
057195072
ABSTRACT:
A 4.times.1 multiplexer for an electrically configurable device uses novel logic gates to logically combine outputs from two SRAM memory cells to control pass gates between the multiplexer signal inputs and a multiplexer output. Each logic gate has three transistors. A complementary NMOS/PMOS pair of transistors defines a transmission gate. The gate of the NMOS transistor defines a first logic-gate input, while the gate of the PMOS transistor defines a second logic-gate input. Their sources are coupled and cooperatively define a third logic-gate input. Their drains are coupled and cooperatively define the logic-gate output. A third transistor, with its gate tied to the third input, couples the logic-gate output to ground when the transmission gate is OFF. The first and second logic-gate inputs are respectively coupled to complementary outputs of one memory cell, while the third logic gate input is coupled to an output of the other memory cell. The memory cells are "pumped" so that their output voltages are at least an NMOS transistor threshold voltage above the maximum signal level at the multiplexer signal inputs. When a logic gate activates its respective pass gate, the pass gate activation voltage is sufficiently high that the pass gate output has the same maximum voltage as the pass gate input. This permits agile tracking of the selected input signal by the multiplexer input, providing high device performance. The logic gates do not require power to be routed to them and require only three transistors each, compared to four for conventional NOR gates. Thus, the present invention achieves high performance while conserving precious integrated circuit area and reducing routing complexity.
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Anderson Clifton L.
Driscoll Benjamin D.
Westin Edward P.
Xilinx , Inc.
Young Edel M.
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