Inmos Limited

Andrew T Ferris

Gordon S Work

A memory circuit comprises a plurality of memory cells (2) arranged in rows and columns, the cells in each row being connected to a common wordline (4) and the cells in each column being connected between a pair of bit lines (6,8) across which a voltage differential is developed when a memory cell is accessed to be read; and a timing circuit (16) for producing a timing signal to control further circuitry in dependence on said voltage differential achieving a predetermined value. The memory circuit has a dummy bit line connected to a column of dummy cells, each dummy cell having the same structure as a memory cell. A plurality of said dummy cells (22) has a bit value stored therein and is connected to a dummy wordline and the remainder of said dummy cells are rendered inactive, whereby on addressing of the dummy wordline simultaneously with the wordline of an accessed cell, a predetermined number of dummy cells discharges via the dummy bit line so that the voltage developed on the dummy bit line bears a predetermined relationship to the voltage differential developed between the bit lines of the accessed cell. The timing circuit (16) is connected to receive the voltage differential on the dummy bit line (18).

Timing control for a memory

A memory circuit comprises a memory array having a plurality of memory cells arranged in rows and columns. Column select circuits enable access to the columns in the array. Each column select circuit is associated with a respective group of the columns and is arranged to access a selected one of the columns in the respective group. At least one spare memory column is provided. Also included are a plurality of read/write circuits associated respectively with the groups, and with the spare memory column, for reading or writing data bits between a data bus and the columns selected by the column selected circuits. Routing circuitry is connected between the read/write circuits and the data bus and is programmable with information identifying at least one faulty column. The routing circuitry is operable in response to an attempted access to the faulty column by disconnecting from the data bus the read/write circuit associated with the group containing the faulty column and connecting to the data bus the read/write circuit associated with the spare column thereby to transfer data between the spare column and the data bus.

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Bristol, United Kingdom

Andrew T Ferris