Hitachi, Ltd.

Hitachi Vlsi Engineering Corp.

Hitachi Microcomputer Engineering, Ltd.

Kikuo Sakai

Masahiro Ogata

Yoshiaki Onishi, Deceased

Satoshi Meguro

Isamu Kobayashi

Toshifumi Takeda

Hiroshi Kawamoto

Takashi Shinoda

Kouichi Nagasawa

Hisahiro Moriuchi

Ryuuji Shibata

Youichi Matsumoto

Hideo Meguro

By Junko Onishi, Administratrix

Junko Onishi, Administratrix

A mask-programmed ROM includes depletion type load MOSFETs provided between data lines in a memory array and a power supply voltage, the MOSFETs having a ground potential of the circuit applied to their gates. Reading of data is carried out by an amplifying MOSFET which supplies a current to a selected data line through a depletion type MOSFET which is supplied at its gate with the circuit ground potential. Thus, bias voltages which are respectively applied to the data lines and a sense amplifier which receives a signal read out from a selected data line are made equal to each other, thereby achieving a high-speed read operation.

Read-only memory

A semiconductor memory includes a dummy cell for forming a reference potential, a read-only memory cell, and a differential amplifier circuit which receives the reference potential formed by the dummy cell and a signal read out from the memory cell. The differential amplifier circuit is dynamically operated so that the semiconductor memory is made smaller in power consumption and size than conventional units. Moreover, in order to reduce the power consumption, the memory cell is brought into the nonselection state when a predetermined time has passed after being selected. In addition, the semiconductor memory is provided with a compensating circuit in order to make the value of the capacitance connected to a word line for transmitting a selecting signal to the memory cell and the value of the capacitance connected to a dummy word line for transmitting a selecting signal to the dummy cell substantially equal to each other. Thus, the changes in potential of both the selecting signals are made substantially equal to each other. Accordingly, it is possible to reduce malfunctions.

Semiconductor device having head only memory with differential amplifier

A semiconductor memory incorporating an ECC circuit includes a memory array, means for selecting a plurality of bits which are to be simultaneously output to the outside of the IC from a plurality of bits which are simultaneously read out from the memory array, and an error correcting circuit which constitutes the ECC circuit. The selecting means is provided in a stage previous to the error correcting circuit. In consequence, it is possible to reduce the number of bits of a signal which need to be simultaneously processed by the error correcting circuit. Accordingly, the size of the ECC circuit can be reduced.

Semiconductor memory with reduced size ECC circuit

YA semiconductor memory is provided with memory cells for storing a plurality of sets of data, each of the sets having check bits. A selecting circuit selects some of the memory cells to form a set in response to a first address signal. The circuit includes an error correcting code circuit, a tristate circuit and a control circuit which forms a control signal to control the tristate circuit. Output terminals of the tristate circuit are coupled with external output terminals of the semiconductor memory. Also, the tristate circuit is controlled by the control signal to bring the external circuit terminals into high impedance at least during the time when the error correcting code circuit is delivering indefinite data.

Semiconductor memory

The address of each defective memory cell in a memory cell array is stored within a semiconductor ROM in advance. In parallel with the operation of reading out information from a memory cell of the array, whether or not the address of the memory cell agrees with the previously stored address of a defective memory cell is distinguished. When they agree, a correcting signal is formed. Erroneous data read out from the defective memory cell is inverted on the basis of the correcting signal and thus corrected, whereupon the corrected data is delivered out of the ROM. In using this error data correcting system, a read-out access time delay caused by furnishing the correcting function corresponds to only one stage of a logic circuit which is used for the inversion to correct the erroneous data. Thus, a semiconductor ROM furnished with an error correcting function can be provided without spoiling enhancement in the speed of the read-out operation.

Semiconductor ROM

Growing community of inventors

Fussa, Japan

Kikuo Sakai