Abstract: A nonvolatile ferroelectric memory device having a multi-bit control function performs read/write operations by selecting a plurality of cells simultaneously, thereby improving the operation speed of a chip. In the nonvolatile ferroelectric memory device, a plurality of cells are selected at the same time, and stable sensing values of data having a small distribution can be obtained by using average characteristics of a plurality of selected cells. Accordingly, since two or more cells are simultaneously selected and a plurality of bits are read/written in the cells depending on stabilized charge, the operation speed of a chip can be improved.

Abstract: A memory has an array made up of transistors that have two charge storage regions between the channel and control gate. Each bit is made up of two charge storage regions that are from different transistors. A bit is written by first erasing all of the storage locations and then writing one of the charge storage locations that make up the bit. A pair of charge storage locations, one erased and the other programmed, is identified for each bit. The logic state of the bit is read by comparing the charge stored in the two charge storage locations that make up the bit. This comparison is achieved by generating signals representative of the charge present in the two charge storage locations. These signals are then coupled to a sense amplifier that functions as a comparator. This avoids many problems that accompany comparisons to a fixed reference.

Abstract: A power-up circuit for an SRAM, particularly a loadless 4-T SRAM cell having PMOS access transistors. The power-up circuit disables a current path to the digit lines in an array of SRAM cells during power-up of the SRAM. As a result, the SRAM cells cannot draw power from the digit lines during power-up if voltages on word lines in the array during power-up cause access transistors for the SRAM cells to become conductive.

Abstract: A Ternary content addressable memory (TCAM) device contain an array differential TCAM cells and a column dummy differential TCAM to enable or disable each corresponding row TCAM cells to compare or not to compare with the input data. A method of sensing the logic state of match or mismatch through comparing the voltage difference of match line and dummy line are presented.

Abstract: The present invention relates to a simplified reference current generator for a magnetic random access memory. The reference current generator is positioned in the vicinity of the memory cells of the magnetic random access memory, and applies reference elements which are the same as the magnetic tunnel junctions of the memory cell and bear the same cross voltages. The plurality of reference elements are used for forming the reference current generator by using one or several bit lines, and the voltage which is the same as the voltage of the memory cell is crossly connected to the reference elements so as to generate a plurality of current signals; and a peripheral IC circuit is used for generating the plurality of midpoint reference current signals and judging the data states. Thanks to the midpoint reference current signals, the multiple-states memory cell, including the 2-states memory cell, can read data more accurately.

Abstract: Using 6 transistor memory cell to replace prior art 10 transistor binary content addressable memory (CAM) cells, and using 10 transistor ternary CAM (TCAM) cell to replace prior art 16 transistor TCAM cells, the present invention provided significant cost saving for high density CAM products. The power consumption problems of prior art high density CAM devices are solved by novel zoned lookup mechanism. For a high density CAM storing sorted data, lookup mechanisms of the present invention can reduce power consumption by two orders of magnitudes.

Abstract: A ternary content addressable memory (TCAM) having an array of cells arranged in rows and columns, each cell comprising of a main memory cell for storing a data bit and its complement and a pair of bit lines for carrying the data bit and its complement. A compare circuit having a pair of compare lines and an output node, the compare circuit coupled to the main memory cell for comparing the data bit and its complement with corresponding compare lines and outputting a compared signal at the output node. A match circuit coupled to the output node of the compare circuit and a match input line and a match output line, the match circuit for selectively connecting the match input line to the match output line based on the compared signal.

Abstract: A content addressable memory (CAM) cell array includes a first-stage memory cell array and a second-stage memory cell array. Only when data on search output lines (match lines) connected to the first-stage memory cell array are coincident, the second-stage memory cell array performs search operation. Therefore, power consumption of the CAM cell array can be reduced.

Abstract: A power-up circuit for an SRAM, particularly a loadless 4-T SRAM cell having PMOS access transistors. The power-up circuit disables a current path to the digit lines in an array of SRAM cells during power-up of the SRAM. As a result, the SRAM cells cannot draw power from the digit lines during power-up if voltages on word lines in the array during power-up cause access transistors for the SRAM cells to become conductive.

Abstract: Architecture, circuitry and method are provided for a ternary content addressable memory (TCAM), and use thereof. Each TCAM cell is relatively small in size. If the TCAM cell is called upon to store voltage values indefinitely, provided power is retained on the cell, the TCAM cell employs no more than 16 transistors. Additional savings in size is achieved by using a single common conductor (or dual common conductors in a differential arrangement) to suffice as both the bit line and compare line. The common bit line and compare line connects to not only the X memory cell, but also the Y memory cell and the compare circuit of the TCAM cell. The compare circuit can either be activated or deactivated. During a compare operation, the compare circuit is selectively activated by placing a ground supply upon a match line enable conductor. The ground supply is imputed upon the match line whenever a mismatch occurs to designate that mismatch.

Abstract: As the number of signaling wires increase in integrated circuits, power consumption, related to charging and discharging of wiring capacitance also increases and emerges as a serious obstacle to the advancement of semiconductor technology. The present invention provides a novel quad-state memory element which can be used as a fundamental building block for designing high speed, high density, and low power integrated circuits.

Abstract: Briefly, in accordance with an embodiment of the invention, a method and an apparatus to program a multi level cell (MLC) phase change material is provided.

Abstract: A method for forming a non-volatile memory (NVM) device, the method including forming two diffusion areas in a substrate, said diffusion areas forming a channel therebetween, the channel being adapted to permit movement of primary electrons to at least one of the diffusion areas, forming a non-conducting charge trapping layer at least over the channel, and managing at least one of movement of secondary electrons from the substrate towards the charge trapping layer and a punch-through voltage in the substrate by controlling a position of a concentration of an electron acceptor dopant in the substrate.

Abstract: Memory cells are used which each have a MOSFET that holds an information voltage of three or more values at its gate, a writing transistor that supplies the information voltage of three or more values to the gate of the MOSFET, and a reading transistor connected in series with the MOSFET. A plurality of reference voltages corresponding to the information voltage of three or more values are applied from a source line to the sources of the MOSFETs, so that digital data is produced by a combination of on-state/off-state of the MOSFET and the plurality of reference voltages or that the source voltages themselves of the MOSFETs are produced as read voltages.

Abstract: A dynamic random access memory for storing one of N levels in each of a plurality of memory cells, the memory cells having storage capacitors coupled to bitline pairs through switches for writing and reading data to and from the memory cells, the memory comprising: at least N−1 bitline pairs, each bitline pair being divided into N−1 sub-bitlines by first switches therebetween; the sub-bitline pairs of each bitline being coupled to adjacent sub-bitline pairs by second switches therebetween, to form N−1 groups of sub-bitlines each for producing one of N−1 reference voltages; sense amplifiers coupled to each sub-bitline pair; N−1 sub-bitline pairs each having reference cells for selective coupling thereto; (N−2)(N−1) sub-bitline pairs each having generate cells for selective coupling thereto; and sub-bitline pairs being selectively connected in a group through switches such that: the sub-bitlines in the group are precharged to one of a plurality of voltages; one of the (

Abstract: A content addressable memory device which determines the top priority entry data without assigning priorities to addresses. If ternary data stored in a cell is invalid data, and other cell at the same bit position stores valid data of entry data identical to an entry key, the entry data is determined not to be a candidate of the top priority entry data. The last entry data which has not determined not to be a candidate is determined to be the top priority data. Compared to the conventional technology which relied on the relationship between a memory address and a priority, the performance of memory system is significantly improved.

Abstract: A memory device having a plurality of memory cells that are group into at least two group of cells. Each cell is capable of being programmed in at least two modes. A mode indicator is associated with each group of cells. The mode indicator indicates which programming mode is used to access the cells. The mode indicator is one or more bits and optionally is user selectable.

Abstract: A method and memory circuits for increasing the data bandwidth per microprocessor operation cycle is provided. The memory circuits provide the additional bandwidth without additional input/output (I/O) pins or requiring decreased cycle times. Multiple bits of data are passed through a single input/output pin with each operation cycle. The multiple bits of data are stored in or retrieved from multiple memory cells in each cycle. The I/O pins carry analog signals which represent multiple values of binary data This method of compressing data can be applied to any device that would benefit from the ability to transfer more data through a limited number of I/O pins.

Abstract: A method and memory circuits for increasing the data bandwidth per microprocessor operation cycle is provided. The memory circuits provide the additional bandwidth without additional input/output (I/O) pins or requiring decreased cycle times. Multiple bits of data are passed through a single input/output pin with each operation cycle. The multiple bits of data are stored in or retrieved from multiple memory cells in each cycle. The I/O pins carry analog signals which represent multiple values of binary data. This method of compressing data can be applied to any device that would benefit from the ability to transfer more data through a limited number of I/O pins.

Abstract: A method and memory circuits for increasing the data bandwidth per microprocessor operation cycle is provided. The memory circuits provide the additional bandwidth without additional input/output (I/O) pins or requiring decreased cycle times. Multiple bits of data are passed through a single input/output pin with each operation cycle. The multiple bits of data are stored in or retrieved from multiple memory cells in each cycle. The I/O pins carry analog signals which represent multiple values of binary data. This method of compressing data can be applied to any device that would benefit from the ability to transfer more data through a limited number of I/O pins.

Abstract: A ternary CAM system includes a main memory cell configured to store complementary data signals D/D#. A first transistor has a source coupled to receive data signal D#, and a gate coupled to receive a compare signal C. A second transistor has a source coupled to receive data signal D, and a gate coupled to receive complementary compare signal C#. A third transistor has a gate coupled to drain regions of the first and second transistors. A mask cell storing a mask value is coupled to the source of the third transistor. A pre-charged match line is coupled to the drain of the third transistor. If compare signals C/C# match data signals D/D#, then the third transistor is turned off, thereby isolating match line and mask cell. If compare signals C/C# don't match data signals D/D#, then the third transistor is turned on, thereby coupling mask cell and match line.

Abstract: According to one embodiment (300) a ternary CAM can include rules stored in CAM locations, where each rule includes match criteria. CAM locations determine priority among various rules. An input value can be matched against stored rules according to the match criteria. In an update operation (300) the CAM can receive a new rule (302). The new rule can be checked for overlap against currently stored rules (304). Rules overlap if an input value exists that can match both rules. If the new rule does not overlap any other rules, it can be added to any free location in the CAM. If the rule overlaps one or more existing rules, the new rule can be stored in an available location that with the appropriate priority with respect to the stored overlapping rules. If no such available location exists, a new set of CAM locations can be randomly selected, and the new rule and all overlapping rules can be written into the selected locations according to priority value.

Abstract: A method and apparatus for determining a longest prefix match in a content addressable memory (CAM) device is described. The CAM device includes a CAM array that may be arbitrarily loaded with CIDR addresses that are not prearranged prior to their entry into the CAM device. For one embodiment, the CAM array is a ternary CAM array that includes CAM cells storing CAM data, mask cells storing prefix mask data for the corresponding CAM cells, a CAM match line for indicating a match between a search key and the CAM data (as masked by the prefix mask data), prefix match lines, and prefix logic circuits for comparing the CAM match line with the prefix mask data. The prefix logic circuits determine the longest prefix among the CAM locations that match the search key, regardless of where the matching locations are logically located in the CAM array.

Abstract: A high-speed sense amplifier includes a pair of cross-coupled inverters coupled to intermediate nodes and then to differential inputs nodes by a control circuit. The intermediate nodes are coupled together by a accelerator transistor that forms a current path when the sense amplifier is placed in a sensing state to provide parallel discharge paths for one or the other of output nodes. During precharge, the accelerator transistor operates to equalize the intermediate nodes to ready them for the next sense phase.

Abstract: A system for storing data in read-only memory is disclosed that comprises bit level conductors, transistors, and sets of reference level conductors. Each reference level conductor has a reference value. A selected reference level conductor transmits a selected reference value to one of the transistors. The transistor transmits the selected reference value to a selected bit level conductor having a selected bit value. The bit level conductors, the transistors and the reference level conductors store data by encoding data as a combination comprising the selected bit value and the selected reference value. A method for storing data in read-only memory is disclosed. Bit level conductors having bit values, transistors, and sets of reference level conductors having reference values are provided. A selected bit value of a selected bit level conductor and a selected reference value of a selected reference level conductor are selected.

Abstract: A load-less 12-T TCAM wherein a TCAM cell uses two 1-bit 4-T SRAM storage cells that are scalable with technology. The TCAM has a TCAM cell that comprises two 1-bit 4-T SRAM data storage cells and a comparator. Within the TCAM cell, each of the two 1-bit 4-T SRAM storage cells is coupled to a BL by a pass-gate PMOS transistor that has a NP drain diode section. This NP drain diode section has a reverse-biased leakage current that is adapted to keep a dynamic node of the SRAM storage cell high without relying on any resistive-load element. The comparator is coupled to these two 1-bit 4-T SRAM storage cells. The comparator is adapted for matching a reference data with data communicated to the comparator from the two SRAM storage cells. The comparator is a 4-T comparator coupled to these two 4-T SRAM storage cells, thereby making the TCAM a 12-T load-less static TCAM.

Abstract: An electrically alterable, non-volatile memory cell has more than two memory states that can be programmed selectively. Programming of the cell is conducted by applying a plurality of programming signals having different characteristics to the cell. The programming signals include at least a first programming signal which programs the cell by a first increment and a subsequent programming signal which programs the cell by a second increment smaller than the first increment. As the cell is being programmed to a selected state, its programming status is verified independently of reference values bounding the memory states. For this purpose, a signal indicative of the programming status (e.g., the cell's bit line signal) is compared with a reference signal corresponding to the selected state but having a value different from the reference value or values bounding the selected state. The programming operation can thus be controlled without actually reading the memory state of the cell.

Abstract: A ternary CAM cell including a binary SRAM CAM cell connected in series with a mask transistor between a match line and a discharge line, and a DRAM mask circuit for applying a mask (care/don't care) value to the gate terminal of the mask transistor. The binary CAM cell stores a data value that is compared with an applied data value, and opens the first portion of a discharge path between the match line and the discharge line when the applied data value fails to match the stored data value. The mask transistor is controlled by the DRAM mask circuit, which includes two associated DRAM memory cells that are connected by a bit line to a sense amplifier. The DRAM mask circuit is refreshed such that, during a read phase of the refresh operation, a data value is read only from the first DRAM memory cell and registered (refreshed) by the sense amplifier circuit. In the subsequent write phase of the refresh operation, the data value is written to the second DRAM memory cell.

Abstract: Memory states of a multi-bit memory cell are demarcated by generating read reference signals having levels that constitute boundaries of the memory states. The read reference signals may be dependent upon the levels of programming reference signals used for controlling the programming of the memory cell. The memory cell can thus be programmed without reading out its memory state during the programming process, with programming margins being assured by the dependence of the read reference signals on the programming reference signals. Both sets of reference signals may be generated by reference cells which track variations in the operating characteristics of the memory cell with changes in conditions, such as temperature and system voltages, to enhance the reliability of memory programming and readout.

Abstract: A four-state (quad) CAM cell that stores one of four logic values: a logic high value, a logic low value, a logic high don't care value, and a logic low don't care value. Each quad CAM cell includes a first memory cell, a second memory cell, a comparator circuit, and a control switch. The first memory cell stores a data value (i.e., logic high value or logic low value), and transmits this stored data value to the comparator circuit. The second memory cell stores a care/don't care data value that is transmitted to the control switch. Portions of the comparator circuit and the control switch form a discharge path between a match line and a discharge line connected to the quad CAM cell. The control switch is controlled by the care/don't care value to open/close a first part of the discharge path. The comparator circuit is controlled to open a second part of the discharge path when, for example, the stored data value is equal to an applied data value.

Abstract: An integrated circuit memory device comprising an arrangement of physical wordlines, WL0-WLn, arrange such that each wordline is addressed by a plurality of pairs, An+1, An, of logical row address bits, and such that at least one pair of logical row address bits, corresponding to physically adjacent wordlines Wlm, Wlm+1, Wlm+2 in succession, cycles between binary states which encode the ternary results A, B and C in succession. The ternary results A, B or C are used to determine which two bitlines of a possible three bitlines are selected by a multiplexer which connects the bitlines to a sense amplifier for determining the state of a bit stored in a memory cell accessed by an activated wordline and a selected bitline. Preferably, the ternary results A, B and C are respectively encoded by said binary states of said pair of logical row address bits, said binary states being “00,” “01,” and “10” respectively.

Abstract: Memories or flip flops used to design today's integrated circuits are based on storing one of two logic states, a first state for indicating a logic one and a second state for indicating a logic zero. Stored logic states are transferred between two-state memories either directly or via Boolean logic gates located between the memories. The transfer of two-state logic signals requires a wire for each unique signal transferred. Moore's Law predicts that the number of transistors per square inch on integrated circuits doubles each 18 months. Thus, potentially the number of two-state memories and signaling wires double each 18 months. As the density of integrated circuits tracks Moore's Law, the wiring within integrated circuit emerges as a serious obstacle to the advancement of semiconductors.

Abstract: A method and memory circuits for increasing the data bandwidth per microprocessor operation cycle is provided. The memory circuits provide the additional bandwidth without additional input/output (I/O) pins or requiring decreased cycle times. Multiple bits of data are passed through a single input/output pin with each operation cycle. The multiple bits of data are stored in or retrieved from multiple memory cells in each cycle. The I/O pins carry analog signals which represent multiple values of binary data. This method of compressing data can be applied to any device that would benefit from the ability to transfer more data through a limited number of I/O pins.

Abstract: A multi-level memory includes an array of memory cells accessible through respective word lines and bit lines a control circuit controlling embedded operations of the memory and a read voltage generating circuit to generate a descending staircase read voltage to a word line associated with a selected memory cell under control of the control circuit. The multi-level memory further includes a read circuit including a latch circuit, and a switch circuit responsive to an evaluate/enable signal to selectively store a read state signal in the latch circuit in response to a sense signal generated from application of the descending staircase read voltage to the word line associated with the selected memory cell.

Abstract: A read only memory integrated semiconductor device includes at least one memory cell. The memory cell includes a storage transistor made within a semiconductor substrate and whose source is connected to ground. A word line is connected to the gate of the transistor. Only one of several bit lines may be connected to the drain of the transistor at a time.

Abstract: The sensing circuits comparing the current flowing in the cell with a plurality of reference currents are not identical to each other but differently amplify the compared currents. In particular, the sensing circuit associated with the lowest reference current amplifies the cell current more than the other sensing circuits and to the respective reference current. The current dynamics is thereby increased and it is possible to keep the reading voltage low, since the inherent characteristic of the lowest reference current may be very close to or directly superimposed on that of the immediately preceding memory cell current distribution, retaining the possibility of discriminating between the different logic levels.

Abstract: A memory device having a plurality of memory cells that are group into at least two group of cells. Each cell is capable of being programmed in at least two modes. A mode indicator is associated with each group of cells. The mode indicator indicates which programming mode is used to access the cells. The mode indicator is one or more bits and optionally is user selectable.

Abstract: The invention discloses a low-power ternary CAM by utilizing four encoded comparand datalines, C0, C1, C2, and C3 in a twin ternary cell. The twin ternary cell is a composite of two ternary CAM bits. The two binary CAM bits are coded so that only one of four comparand datalines is toggled during a compare operation. The encoded data is stored and used for comparison. In one embodiment, the four possible states for the 2 bit comparands are coded as 0001, 0010, 0100, and 1000.

Abstract: A two-dimensional memory comprises a matrix of multi-valued resonant tunneling diodes (RTD). Each memory cell has two series RTDs with hysteretic folding V-I characteristics. The memory state is determined by the node voltage between the two RTDs and the series current. Each memory cell has two terminals connected to two bit lines through word line switches. The two bit lines are fed with two sets of multi-valued data and are written into the cell by two consecutive pulses to set the operating point. The two sets of multi-valued data are converted by two D/A converters from two sub-words of the binary digital word. The memory state is read by the sensing the voltages at the two terminals, or voltage at one terminal and the current through the other terminal.

Abstract: The present invention provides a multi-value DRAM that does not require additional surface area, has a low cost, and has a good yield. A 4-value memory cell is disposed at the intersection of a word line WL and sub-bit lines BLNx0. A potential corresponding to 11, 10, 01, and 00 is written to the dunmmy cell disposed at the intersection of the sub-bitline connected to the dummy word lines DWLN and DWLT and the SSAs 31 and 32. The SSA30 outputs the data in the memory cell and the reference levels 0x and 1x on the sub-bit lines BLTx0 to the main bit lines GBLN0 and GBLT0. The SSA31 balances the potentials of the dummy cell connected to both dummy word lines and outputs the reference levels 11 and 10 to the main bit line GBLN4. Similarly, the SSA32 balances the potentials of both dummy cells, and outputs the reference levels 01 and 00 to the main bit line GBLT4. The MSA 33 discriminates the upper bit UPBIT and the lower bit LWBIT of the data based on the potentials on the 4 main bit lines.

Abstract: Disclosed is a data storage device capable of storing plural bits of data using one storage circuit which can hold two signal levels.

Abstract: A memory device having a sense trigger coupled to receive an address when available, and to assert a sense trigger signal to the sense trigger when the sense trigger receives the address. The memory device also has an N-NARY, or 1-of-N, input logic gate that provides additional assurance that no more than one word line is asserted when an address is decoded. The memory device also has an N-NARY, or 1-of-N, output driver logic gate that provides an output signal directly useful for providing to another (N-NARY) 1-of-N logic gate.

Abstract: A reading circuit for a multibit memory cell in a memory array, the memory cell having a threshold gate voltage within a range of one of a first, second, third and fourth predetermined threshold voltages corresponding respectively to one of four states of two bits stored in the memory cell. The reading circuit includes a circuit to provide a gate voltage to the multibit memory cell during a read cycle, the gate voltage having a first level between the second and third predetermined threshold voltages during a first time interval of the read cycle and a second level between the third and fourth predetermined threshold voltages during a second time interval of the read cycle.

Abstract: A nonvolatile semiconductor memory device includes nonvolatile memory cells (C), constant voltage circuits for applying one of different verify voltages to control gates of the nonvolatile memory cells C in response to control data introduced into the memory device from the exterior, and writing and sensing circuit circuits for applying a potential to drains of the nonvolatile memory cells C in response to write data introduced into the memory device and for detecting and amplifying currents between drains and sources of the nonvolatile memory cells. By dividing the memory cell array 501 and a serial register 502 into some parts and by connecting an external SRAM 503 so as to progress the transfer of data from the memory cell array 501 to the serial register 502 and the transfer of data from the serial register 502 to the external SRAM 503 in parallel, the read speed is increased.

Abstract: Data buses are arranged in a one-to-one correspondence to pads. These data buses are arranged in common to a plurality of memory arrays. A read data driver is rendered active selectively according to a word configuration to switch equivalently the connection between a memory array and a data bus.

Abstract: A reading circuit for a multibit memory cell in a memory array, the memory cell having a threshold gate voltage within a range of one of a first, second, third and fourth predetermined threshold voltages corresponding respectively to one of four states of two bits stored in the memory cell.

Abstract: A ternary content addressable memory (CAM) cell. For one embodiment, the ternary CAM cell includes a first memory cell, a compare circuit, a second memory cell and a mask circuit. The first memory cell is coupled to a first pair of bit lines that carries data to and from the first memory cell. The compare circuit receives comparand data on a pair of compare signal lines, and compares the comparand data with the data stored in the first memory cell. The compare circuit includes a pair of transistors and a match transistor. The pair of transistors receives the comparand data on the compare signal lines and also receives the data stored in the first memory cell. The match transistor determines the state of a match line. The second memory cell stores mask data that may mask the comparison result such that it does not affect the logical state of the match line.

Abstract: Memory states of a multi-bit memory cell are demarcated by generating read reference signals having levels that constitute boundaries of the memory states. The read reference signals are dependent upon the levels of programming reference signals used for controlling the programming of the memory cell. The memory cell can thus be programmed without reading out its memory state during the programming process, with programming margins being assured by the dependence of the read reference signals on the programming reference signals. Both sets of reference signals may be generated by reference cells which track variations in the operating characteristics of the memory cell with changes in conditions, such as temperature and system voltages, to enhance the reliability of memory programming and readout.

Abstract: A method of processing data having one of four voltage levels stored in a DRAM cell is comprised of sensing whether or not the data voltage is above or below a voltage level midway between a highest and a lowest of the four levels, setting the voltage on a reference line higher than the lowest and lower than the next highest of the four levels in the event the data voltage is below the midway voltage level, and setting the voltage on the reference line higher than the second highest and lower than the highest of the four levels in the event the data voltage is above the midway point, and sensing whether the data voltage is higher or lower than the reference line, whereby which of the four levels the data occupies is read.

Abstract: A sensing circuit for serial dichotomic sensing of multiple-level memory cells which can take one programming level among a plurality of m=2n (n>=2) different programming levels, comprises biasing means for biasing a memory cell to be sensed in a predetermined condition, so that the memory cell sinks a cell current with a value belonging to a plurality of m distinct cell current values, each cell current value corresponding to one of the programming levels, a current comparator for comparing the cell current with a reference current generated by a variable reference current generator, and a successive approximation register supplied with an output signal of the current comparator and controlling the variable reference current generator.