Inmos Limited

Rahul Sud

Kim Carver Hardee

John D Heightley

John O Heightley

A bootstrap driver circuit is used asynchronously in a static RAM. A capacitor is coupled between second and third nodes, and a charge pump is coupled to provide charge to the second node. Address bits can be applied to the gates of respective transistors whose drains form a common node coupled to the source of a low impedance transistor whose drain is coupled to a first node. An inverter is coupled to the common node for applying a delayed input signal to the gates of first and second enhancement mode transistors. This provides a discharge path for the third node in response to a low level memory address signal thereby to maintain a differential voltage across the bootstrap capacitor. Also disclosed is an input protection circuit when the bootstrap driver is used as a chip select buffer. A timing circuit receives an input signal and develops a first signal and a delayed signal, both of which are applied to the bootstrap driver. One embodiment particularly useful for overcoming gliches on an input signal uses a charge pump, a latch and release network, an inverting buffer, and a bootstrap isolation transistor. An early discharge transistor and a late discharge transistor provide a discharge path for the isolation transistor. The early discharge transistor is responsively coupled to the digital input signal, and the late discharge transistor is responsively coupled to the output of the inverting buffer.

Bootstrap driver for a static RAM

A low power I/O scheme is described which is particularly useful in wide word semiconductor memories which include redundant memory cells as well as regular memory cells. In the present scheme, conventional load transistors for a main data bus are turned off during all write operations to conserve power. In addition, predata lines which carry data between memory cells and the main data buss include load transistors that are turned off during normal read or write operations to conserve additional power, and turned on during spare read or write operations to preserve the stability of unselected regular cells. The predata lines are also preferably held above ground potential during read or write operations to prevent conduction of deselected column select transistors.

Low power I/O scheme for semiconductor memories

A bootstrap driver circuit is used asynchronously in a static RAM. A capacitor is coupled between second and third nodes, and a charge pump is coupled to provide charge to the second node. Address bits can be applied to the gates of respective transistors whose drains form a common node coupled to the source of a low impedance transistor whose drain is coupled to a first node. An inverter is coupled to the common node for applying a delayed input signal to the gates of first and second enhancement mode transistors. This provides a discharge path for the third node in response to a low level memory address signal thereby to maintain a differential voltage across the bootstrap capacitor. Also disclosed is an input protection circuit when the bootstrap driver is used as a chip select buffer. A timing circuit receives an input signal and develops a first signal and a delayed signal, both of which are applied to the bootstrap driver. One embodiment particularly useful for overcoming glitches on an input signal uses a charge pump, a latch and release network, an inverting buffer, and a bootstrap isolation transistor. An early discharge transistor and a late discharge transistor provide a discharge path for the isolation transistor. The early discharge transistor is responsively coupled to the digital input signal, and the late discharge transistor is responsively coupled to the output of the inverting buffer.

Bootstrap driver circuits for an MOS memory

A circuit is described for precharging and equilibrating the bit lines in a semiconductor memory. The circuit includes a pair of precharging transistors, each coupled between its own bit line and a common node, and each adapted to receive a precharging pulse at its gate. A transistor circuit is coupled to the common node to establish thereat a variable operating potential such that when the precharging pulse occurs, one of the precharging transistors conducts to raise its bit line to a precharge potential while simultaneously reducing the operating potential at the common node. The lower voltage at the common node permits the other precharging transistor to conduct so that its bit line is precharged and both bit lines are equilibrated through the conducting transistors.

Bit line precharging and equilibrating circuit

A redundancy system is described for a high speed, wide-word semiconductor memory having first and second arrays of regular memory cells. The system includes a plurality of spare columns of cells, half of which are located adjacent the first array and half of which are located adjacent the second array. The number of spare columns which are adjacent each array is equal to the number of regular columns which are simultaneously selectable by an address input. Circuitry is included for responding to an incoming address representative of a defective regular cell for selecting half the spare columns in the first array in lieu of the regular addressed columns therein, and for selecting half the spare columns in the second array in lieu of the addressed regular columns therein.

Redundancy system for high speed, wide-word semiconductor memories

A static RAM (random access memory) is described wherein fully asynchronous active equilibration and precharging of the RAM's bit lines provides improved memory access time and lower active power dissipation. In the preferred embodiment, each change in the memory's row address is sensed for developing a clock pulse of a controlled duration. The clock pulse is received by a group of equilibrating transistors and a group of precharging transistors which are coupled to the memory's bit lines. When the clock pulse occurs, all the abovementioned transistors conduct to effect simultaneous equilibration and pre-charging of the bit lines.

Asynchronously equillibrated and pre-charged static ram

A redundancy scheme is described for use with an MOS memory having a main array of memory cells, and a plurality of spare memory cells. Typically, each memory cell is tested for operability by a conventional probe test. When a defective memory cell is found, an on-chip address controller responds to the probe test finding a defective cell by permanently storing and rendering continuously available a fully asynchronous electrical indication of the address of the defective cell. The address controller compares its stored data with memory cell information received during normal memory operation, and generates a control signal indicative of the receipt of an address which corresponds to a defective cell. A spare cell selector responds to the control signal by electrically accessing a spare memory cell and by prohibiting access of the defective memory cell.

Redundancy scheme for an MOS memory

A substrate bias generator for an integrated circuit, metal-oxide-semiconductor (MOS) random access memory (RAM) is described. The on-chip generator includes two input terminals for receiving first and second trains of periodic pulses. The periodic pulses have the same frequency and are phase synchronized. However, the first train of pulses has a greater duty cycle than the second train of pulses. Amplitude transitions associated with the first and second trains of pulses are capacitively coupled to first and second nodes, respectively. A pair of transistors are coupled to the nodes, one transistor for clamping the first node to ground when the second node receives a positive-going voltage transition, and another transistor for selectively coupling amplitude transitions from the first node to the second node. In operation, both nodes are driven more negative with each successive incoming pulse until they reach about -5 volts for the case in which the amplitude of the incoming pulses is 5 volts. A third transistor closes a current path between the first node and the chip's substrate when the substrate voltage is at least one threshold voltage more positive than the first node voltage. As a result, the substrate voltage is driven to a negative level which is about one threshold voltage more positive than the furthest negative voltage level on the first node.

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Colorado Springs, CO, United States of America

Rahul Sud