Kabushiki Kaisha Toshiba

Tokyo Shibaura Denki Kabushiki Kaisha

Microcomputer Engineering Ltd.

Shaibaura Denki Kabushiki Kaisha

Mitsuo Isobe

Takayuki Ohtani

Takayasu Sakurai

Hisashi Ueno

Masataka Matsui

Tetsuya Iizuka

Akira Aono

Jun-ichi Tsujimoto

Takayuki Ootani

Kazuhiro Sawada

Makiji Kobayashi

Kazutaka Nogami

Shigeyuki Hayakawa

Naohiro Matsukawa

Azuma Suzuki

Tohru Kimura

Tatsuya Inatsuki

Takahiro Hamano

Shinich Nakauchida

Nobuaki Urakawa

A refresh control circuit for a pseudo static random access memory includes a refresh control signal output circuit for outputting a refresh control signal to accomplish refresh control of the pseudo static random access memory, and includes a delay circuit. A first chip enable signal from a control device such as a MPU is delayed by the delay circuit and outputted as a second chip enable signal for the PSRAM. As the first chip enable signal level changes from a selection level to a non-selection level, the refresh control signal level changes to a non-refresh level. This state is maintained for a predetermined period. After the second chip enable signal changes from the selection level to the non-selection level, the refresh control signal returns from the non-refresh level to the refresh level. Thus, the PSRAM enters into the refresh state during the non-selection state, and is refreshed. This refresh operation is necessarily performed after an access to PSRAM.

Refresh control circuit of pseudo static random access memory and pseudo

A refresh control circuit for a pseudo static random access memory includes a refresh control signal output circuit for outputting a refresh control signal to accomplish refresh control of the pseudo static random access memory, and includes a delay circuit. A first chip enable signal from a control device such as a MPU is delayed by the delay circuit and outputted as a second chip enable signal for the PSRAM. As the first chip enable signal level changes from a selection level to a non-selection level, the refresh control signal level also changes to a non-refresh level. This state is maintained for a predetermined period. After the second chip enable signal changes from the selection level to the non-selection level, the refresh control signal returns from the non-refresh level to the refresh level. Thus, the PSRAM enters into the refresh state during the non-selection state, and is refreshed. This refresh operation is necessarily performed after an access to PSRAM.

A semiconductor memory device has a memory cell matrix in which a plurality of memory cells are connected in rows by work lines and in columns by bit lines. The device comprises cell row groups each of which is formed by memory cell rows commonly activated by several row address signals at a first selection stage, a row group selection decoder having the smallest decoding circuits as a first stage decoder each connected to the row group(s) by first stage word line and commonly activating any group(s) at the first row selection stage by several row address signals, and a row selection decoder as a second stage decoder having the smallest decoding units entirely provided in the matrix and each activating any cell row(s) at a second selection stage by remaining row address signals.

Semiconductor memory device having two-dimensional matrix array

A semiconductor memory having dynamic memory cells includes a determining circuit for determining whether or not it is necessary to refresh the dynamic memory cells, and only when it is necessary, outputting a refresh execution signal in response to a refresh request signal from an external circuit, and a circuit for executing a refresh operation in response to the refresh execution signal. Even if the refresh request signal is supplied, a refresh operation is not executed unless the determining circuit determines that the refresh operation is necessary, thus dispensing with unnecessary refresh operations. Preferably, the determining circuit includes a timer which outputs a signal at every predetermined period. Only when the signal is output from the timer, is the refresh request signal from an external circuit accepted and the refresh execution signal output.

Semiconductor memory

A main row decoder for driving main word lines in a main memory cell array includes partial decoders the number of which is equal to the number of the main word lines. Each partial decoder includes a NAND gate for receiving row address signals, an inverter for driving a corresponding main word line in response to an output from the NAND gate, a fuse element connected between the output terminal of the NAND gate and the input terminal of the inverter, and a MOS transistor connected between the input terminal of the inverter and a power supply voltage.

Semiconductor memory device

During a data-clearing operation, while maintaining in the OFF state the transfer gate transistors in each of the static type memory cells associated with at least one column, the source of one of two drive transistors incorporated in the memory cell is set to a high potential level, and the source of the other drive transistor to a low level. As a result, the clearing operation is performed to a minimum of 1 column in the memory cell matrix. Due to the arrangement of the memory device, no address-selecting operation is required for selecting a memory cell during the clearing operation. Moreover, the clearing operation is carried out in a minimum unit of 1 column in the memory cell matrix. Consequently, the processing time for the clearing operation is reduced. Furthermore, the DC current flowing during the clearing operation is reduced, since the transfer gate transistor in the memory cell is maintained in the OFF state during the clearing operation, with the result that the power consumption is lowered.

Semiconductor memory device with a potential level-setting circuit

A control signal output circuit for outputting a control signal in response to first and second input signals and a power source voltage, comprises an inverter which inverts one of the first and second input signals and outputs an inverted signal. The control signal output circuit further comprises a logic circuit which outputs a control signal in response to the inverted signal and the other of the first and second input signals. A switch is further provided to disconnect the inverter from the power source voltage in response to the other of the first and second input signals.

Control signal output circuit

A virtual type static semiconductor memory device according to the present invention comprises a refresh detector circuit for detecting the enabling operation of a refresh control circuit and a terminal for outputting to an outside a detection signal which is generated from the refresh detector circuit. The virtual type static semiconductor memory device informs a present refresh operation to the outside when it is accessed from the outside during the time period in which a refresh operation is conducted in the semiconductor memory device. A system employing the semiconductor memory device allows a slow access at that time only and allows access to be gained to the semiconductor memory device at high speed at other times.

Virtual type static semiconductor memory device including refresh

An output circuit for outputting an output signal in response to an input signal having first and second voltage levels, comprises first circuit responsive to the input signal for generating a first signal including a low impedance portion corresponding to the duration of the second level of the input signal. A second circuit responsive to the input signal is further provided to supply a second signal including a low impedance portion which exists after the duration of the second voltage level of the input signal. The first and the second signals are combined to produce the output signal.

Output circuit for a semiconductor device for reducing rise time of an

A static semiconductor memory comprises a word line, a memory cell array divided into a plurality of blocks in an extending direction of the word line, each block including a plurality of sections each of which includes a plurality of static memory cells, a controller, a section data line provided for each section, first sense amplifiers, a block data line provided for each block, second sense amplifiers, a main data line and a latch circuit for latching data on the main data line. The controller selects an arbitrary section in the memory cell array at the time of data readout and controls the reading of data from memory cells included in the selected section. The section data line is supplied with data read out from the memory cells. The first sense amplifiers, coupled at their input terminals to the section data line, are activated only when their associated section is selected. The individual first sense amplifiers in the same block have their output terminals commonly coupled to the block data line. Each second sense amplifier, coupled at its input terminal to the associated block data line, is activated only when the sections belonging to that block are selected. The second sense amplifiers have their output terminals commonly coupled to the main data line.

Static semiconductor memory with section and block sense amplifiers

A precharge circuit is provided between bit lines, on the one hand, and a power source potential on the other. The precharge circuit is controlled to be conductive/nonconductive by a clear signal. A control unit is also provided, which controls a decoder when the clear signal is supplied so as to set all the word lines in a selective state. In a clear mode, writing circuits write the same data simultaneously into all of the memory cells.

A semiconductor memory device comprising a memory cell-selecting section, an input supply control section, and a bit-line potential control section. The memory cell-selecting section includes a row decoder and a first gate circuit coupled to the output thereof. The memory cell-selecting section drives all the memory cells making up the memory device, when it is set in the mode for clearing the memory device, and the input data supply control section disconnects a pair of bit lines from a write circuit when the control section is set in this same mode. When the bit-line potential control section is set in the memory-clearing mode, it sets the potential of one of the bit lines at a high level, and the potential of the other bit line at a low potential.

Semiconductor memory device with a data clear circuit

In an output buffer control circuit of a memory, the set/reset state of a flip-flop is controlled by an address transition detection output and a read detection output supplied when completion of data read from a memory cell is detected, and the active/inactive state of an output buffer for outputting the readout data from the memory cell is controlled by an output from the flip-flop. According to this arrangement, when an address input transits and the address transition detection output is enabled, the output buffer is inactivated. When data is read out from the memory cell and the read detection output is enabled after the address input transits, the output buffer can be activated.

Output buffer control circuit of memory device

A defect detection circuit for detecting a defect of a memory cell, a counter for counting defects detected by the defect detect circuit, and a remediableness determination unit for determining whether a count of the counter allows remedy by a redundancy circuit, are provided in a tester for a semiconductor memory or on a memory chip having a redundancy circuit. When the count of the counter is the same as or smaller than the number of at least one of the auxiliary rows and columns of the redundancy circuit, the memory is determined to be 'remediable.' Otherwise, the memory is determined to be 'unremediable.' When the count of the counter exceeds the number of at least one of the auxiliary rows and columns of the redundancy circuit, the memory test is interrupted.

Semiconductor memory device having a self-diagnosing function

The threshold voltage of bit line percharge/equalize MOS transistors is smaller than that of normally ON type bit line pull-up transistors. With this feature, there is no current flows through a bit line from power source V.sub.DD during a read-out operation. The voltage difference between a pair of bit lines can be increased at high speed, thereby increasing the read-out speed.

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Tama, Japan

Mitsuo Isobe