Stmicroelectronics S.r.l.

Sgs-thomson Microelectronics S.r.l.

Ernestina Chioffi

Marco Pasotti

Roberto Antonio Canegallo

Pier Luigi Rolandi

Danilo Gerna

Giovanni Guaitini

Gianluca Colli

Alfredo Tomasini

Pierluigi Rolandi

Frank Lhermet

Cedric Issartel

For each memory cell to be programmed, the present threshold value of the cell is determined; the desired threshold value is acquired; the analog distance between the present threshold value and the desired threshold value is calculated; and a programming pulse is then generated, the duration of which is proportional to the analog distance calculated. The programming and reading cycle is repeated until the desired threshold is reached. By this means a time saving is obtained, owing to the reduction of the number of intermediate reading steps. The method permits programming in parallel and simultaneously of a plurality of cells of a memory array which is connected to a single word line and to different bit lines, each with a programming pulse the duration of which is proportional to the analog distance calculated for the same cell. The programming process is thus very fast, owing to parallel application of the programming and the saving in the intermediate reading cycles.

Method and device for analog programming of non-volatile memory cells

The controlled erase method includes supplying at least one erase pulse to cells of a memory array; comparing the threshold voltage of the erased cells with a low threshold value; selectively soft-programming the erased cells which have a threshold voltage lower than the low threshold value; and verifying whether the erased cells have a threshold voltage lower than a high threshold value, which is higher than the low threshold value. If at least one predetermined number of erased cells has a threshold voltage which is higher than the high threshold value, an erase pulse is applied to all the cells and the steps of comparing, selectively soft-programming and verifying are repeated.

Method for controlled erasing memory devices, in particular analog and

A device for analog programming is disclosed. The device comprises a current mirror circuit connected to drain terminals of a cell to be programmed and of a MOS reference transistor. An operational amplifier has inputs connected to the drain terminals of the cell and respectively of the MOS transistor and an output connected to the control terminal of the MOS transistor. During programming, the control and drain terminals of the cell are biased at corresponding programming voltages and the output voltage of the operational amplifier, which is correlated to the current threshold voltage level of the cell, is monitored and the programming is interrupted when this output voltage becomes at least equal to a reference voltage correlated to the threshold value desired for the cell.

Method and device for analog programming of flash EEPROM memory cells

The programming method comprises the steps of applying a programming pulse to a first cell and simultaneously verifying the present threshold value of at least a second cell; then verifying the present threshold value of the first cell and simultaneously applying a programming pulse to the second cell. In practice, during the entire programming operation, the gate terminal of both the cells is biased to a same predetermined gate voltage and the source terminal is connected to ground; the step of applying a programming pulse is carried out by biasing the drain terminal of the cell to a predetermined programming voltage and the step of verifying is carried out by biasing the drain terminal of the cell to a read voltage different from the programming voltage. Thereby, switching between the step of applying a programming pulse and verifying is obtained simply by switching the drain voltage of the cells.

Method for parallel programming of nonvolatile memory devices, in

The reading circuit comprises a current source, which, via a current reflection circuit, supplies a constant predetermined current to a cell to be read, an operational amplifier with a non-inverting input connected to the drain terminal of the cell, and an output connected to the gate terminal of the cell. The source terminal of the cell is connected to ground. Thereby the output voltage of the operational amplifier supplies directly (at the set current) the threshold voltage of the cell, and the drain terminal of the cell is biased to a positive voltage.

Reading circuit for nonvolatile analog memories, in particular

An analog reading circuit having a current mirror circuit forcing two identical currents into a cell to be read and into a reference cell. An operational amplifier has an inverting input connected to the drain terminal of the cell to be read, a non-inverting input connected to the drain terminal of the reference cell, and an output connected to the gate terminal of the reference cell. The reference cell therefore forms part of a negative feedback loop which maintains the overdrive voltages of the cell to be read and the reference cell constant, irrespective of temperature variations. The reading circuit is also of high precision and has a high reading speed.

High-precision analog reading circuit for flash analog memory arrays

A programming method for a nonvolatile memory includes the steps of: a) determining a current value of the threshold voltage; b) acquiring a target value of the threshold voltage; c) calculating a first number of gate voltage pulses necessary to take the threshold voltage from the current value to the target value; d) applying a second number of consecutive voltage pulses to the gate terminal of the cell, the second number being correlated to the first number and having a uniformly increasing amplitude; e) then measuring a current value of the threshold voltage; and repeating steps c) to e) until a final threshold value is obtained.

Method for multilevel programming of a nonvolatile memory, and a

An integrated image processing system includes an array of cells arranged in rows and columns. Each cell corresponds to a pixel of an image and includes a photosensitive element for detecting the luminous intensity of its respective pixel and for generating a value. A first switch controls the transfer of the value from a respective photosensitive element to the corresponding capacitor, which stores the value. A second switch couples each of the cells in parallel to a common line. A control circuit receives the values from each cell on the common line and generates a signal for regulating the switching time interval of the first switch.

Adaptive optical sensor

A reading circuit comprises a current mirror circuit connected, at a first and a second output node, to the drain terminals of an array cell and of a reference cell; a comparator whose inputs are connected to the output nodes of the current mirror circuit; a ramp generator having an enabling input connected to the output of the comparator and an output connected to the control terminal of the reference cell. Biasing the gate terminal of the array cell to a constant voltage, when the currents flowing in the array cell and in the reference cell are equal, the value assumed by the ramp voltage is proportional to the threshold value of the array cell; at that time the comparator is triggered and discontinues the ramp increase, supplying as output the desired threshold value.

Circuit and method of reading cells of an analog memory array, in

A method and a respective circuit arrangement capable of markedly limiting the absorption of current by a current comparator circuit. The invention consists in limiting the absorption of current through the branch of the comparator circuit, along which is forced the highest current to the value of the lowest current, which is in turn forced through the other branch of the comparator circuit. This condition is obtained without interfering in any way with other characteristics of switching speed and sensitivity of the comparator circuit.

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Pavia, Italy

Ernestina Chioffi