Multiple-valued mask programmable read only memory semiconductor device with improved word level generator
First Claim
1. A word level generator in a multiple-valued mask programmable read only memory semiconductor device having a plurality of kinds of mask programmable read only memory cells having a plurality of distributions in number of the mask programmable read only memory cells versus variation of actual threshold voltages from predetermined threshold voltages, and the distributions being separated from each other and having no overlap to each other,wherein the word level generator generates signals corresponding to a maximum voltage level of a lower one of an adjacent two of the distributions and a minimum voltage level of a higher one of the adjacent two of the distributions and generates a word level between the maximum and minimum voltage levels.
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Abstract
A word level generator in a multiple-valued mask programmable read only memory semiconductor device having a plurality of kinds of mask programmable read only memory cells having a plurality of distributions in number of the mask programmable read only memory cells versus variation of actual threshold voltages from predetermined threshold voltages. The distributions are separated from each other and do not overlap each other. The word level generator generates a word level which is between a maximum voltage level of lower one of adjacent two of the distributions and a minimum voltage level of higher one of the adjacent two of the distributions, so that all of the mask programmable read only memory cells are permitted to show correct ON/OFF operations for application of different word level voltages, whereby only correct data are obtained from the multiple-valued mask programmable read only memory semiconductor device.
61 Citations
31 Claims
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1. A word level generator in a multiple-valued mask programmable read only memory semiconductor device having a plurality of kinds of mask programmable read only memory cells having a plurality of distributions in number of the mask programmable read only memory cells versus variation of actual threshold voltages from predetermined threshold voltages, and the distributions being separated from each other and having no overlap to each other,
wherein the word level generator generates signals corresponding to a maximum voltage level of a lower one of an adjacent two of the distributions and a minimum voltage level of a higher one of the adjacent two of the distributions and generates a word level between the maximum and minimum voltage levels.
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4. A word level generator for a multi-valued programmable read only semiconductor memory device that has plural kinds of programmable read only memory cells, each of the plural kinds of cells having a distribution of a number of such cells versus a variation of actual threshold voltage from a defined threshold voltage, the distributions being separate from each other so that a maximum voltage value of a lower one of an adjacent pair of the distributions does not overlap a minimum voltage value of a minimum voltage of a higher one of the adjacent pair, the word level generator comprising:
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a first reference level generator circuit for generating a first reference level which corresponds to the maximum value of the lower distribution; a second reference level generator circuit for generating a second reference level which corresponds to the minimum value of the higher distribution; and a word level generator circuit connected to the first and second reference level generator circuits for receiving the first and second reference levels from the first and second reference level generator circuits and for generating the word level which lies between the first and second reference levels. - View Dependent Claims (5, 6, 7, 8, 9, 10)
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11. A device for generating a word level that is both higher than a maximum voltage value of a first distribution in threshold voltage of first type mask programmable read only memory cells intended to have a first threshold voltage and lower than a minimum voltage value of a second distribution in threshold voltage of second type mask programmable read only memory cells intended to have a second threshold voltage, the first and second distributions being adjacent to each other and separated from each other to have no overlap so that the first distribution is lower in threshold voltage than the second distribution,
the device comprising means for generating signals corresponding to the maximum and minimum voltage values and for generating the word level therebetween using the corresponding signals.
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14. A device for generating a word level that is both higher than a maximum voltage value of a first distribution in threshold voltage of first type mask programmable read only memory cells intended to have a first threshold voltage and lower than a minimum voltage value of a second distribution in threshold voltage of second type mask programmable read only memory cells intended to have a second threshold voltage, the first and second distributions being adjacent to each other and separated from each other to have no overlap so that the first distribution is lower in threshold voltage than the second distribution, the device comprising:
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a first reference level generator circuit for generating a first reference level which corresponds to the maximum value of the first distribution; a second reference level generator circuit for generating a second reference level which corresponds to the minimum value of the second distribution; and a word level generator connected to the first and second reference level generator circuits for receiving the first and second reference levels from the first and second reference level generator circuits and for generating the word level which lies between the first and second reference levels. - View Dependent Claims (15, 16, 17, 18, 19, 20)
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21. A multiple-valued mask programmable read only memory semiconductor device comprising:
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a memory cell array including a plurality of kinds of mask programmable read only memory cells having a plurality of distributions in number of the mask programmable read only memory cells versus variation of actual threshold voltages from predetermined threshold voltages, and the distributions being separated from each other and having no overlap to each other; a sense amplifier connected to the mask programmable read only memory cells for sensing ON/OFF states of said mask programmable read only memory cells; a plurality of latch circuits connected to the sense amplifier for receiving output signals about the ON/OFF states from said sense amplifier to hold the output signals; a decoder circuit connected to the latch circuits for receiving the output signals from the latch circuits to decode the output signals into data about the ON/OFF states; a plurality of output buffer circuits connected to the decoder circuit for outputting the data about the ON/OFF states; and a word level generator connected to gates of the mask programmable read only memory cells for supplying at least one word level for controlling ON/OFF states of said mask programmable read only memory cells, wherein the word level generator generates voltages corresponding to a maximum voltage level of a lower one of an adjacent two of the distributions and a minimum voltage level of a higher one of the adjacent two of the distributions and generates a word level between the maximum and minimum voltage levels. - View Dependent Claims (22, 23)
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24. A multiple-valued mask programmable read only memory semiconductor device comprising:
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a memory cell array including a plurality of kinds of mask programmable read only memory cells having a plurality of distributions in number of the mask programmable read only memory cells versus variation of actual threshold voltages from predetermined threshold voltages, and the distributions being separated from each other and having no overlap to each other; a sense amplifier connected to the mask programmable read only memory cells for sensing ON/OFF states of said mask programmable read only memory cells; a plurality of latch circuits connected to the sense amplifier for receiving output signals about the ON/OFF states from said sense amplifier to hold the output signals; a decoder circuit connected to the latch circuits for receiving the output signals from the latch circuits to decode the output signals into data about the ON/OFF states; a plurality of output buffer circuits connected to the decoder circuit for outputting the data about the ON/OFF states; and a word level generator connected to gates of the mask programmable read only memory cells for supplying at least one word level for controlling ON/OFF states of said mask programmable read only memory cells, wherein the word level generator generates voltages corresponding to a maximum voltage level of a lower one of an adjacent two of the distributions and a minimum voltage level of a higher one of the adjacent two of the distributions and generates a word level between the maximum and minimum voltage levels, wherein the word level generator comprises, a first reference level generator circuit for generating a first reference level which corresponds to the maximum value of the lower distribution, a second reference level generator circuit for generating a second reference level which corresponds to the minimum value of the higher distribution, and a word level generator circuit connected to the first and second reference level generator circuits for receiving the first and second reference levels from the first and second reference level generator circuits in order to generate the word level which lies between the first and second reference levels. - View Dependent Claims (25, 26, 27, 28, 29, 30)
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31. A method of determining a word level that is both higher than a maximum voltage value of a first distribution in threshold voltage of first type mask programmable read only memory cells intended to have a first threshold voltage and lower than a minimum voltage value of a second distribution in threshold voltage of second type mask programmable read only memory cells intended to have a second threshold voltage, provided that the first and second distributions are separated from each other to have no overlap so that the first distribution is lower in threshold voltage than the second distribution,
the method comprising the steps of generating signals corresponding to the maximum and minimum voltage values, and generating the word level using the corresponding voltages.
Specification