Texas Instruments Corporation

Tim M Coffman

Sung-Wei Lin

Phat C Truong

T Damodar Reddy

Dennis R Robinson

Ronald J Syzdek

Timothy J Coots

John Frederic Schreck

David D Wilmoth

George Ernest Harris

Jeffrey K Kaszubinski

Ming-Bo Liu

A floating-gate memory which uses a skewed reference for sensing. The skewed reference preferably has a substantially different VT implant dose than the array cells, and can also have different sizing.

Balanced reference sensing circuit

A supply-voltage detecting stage (11) that supplies first and second reference currents (I.sub.REFP and I.sub.REFN) which vary with the supply voltage (V.sub.cc) and are coupled by first and second gain stages (12A and 12B), respectively, to first and second temperature-detecting stages (13A and 13B), respectively. First and second temperature-detecting stages (13A and 13B) increase the coupled reference currents (I.sub.REFP and I.sub.REFN), respectively, to compensate for temperature increase through use temperature-sensitive, long-channel transistors (M34-M37 and M42-M45), supplying temperature and supply-voltage compensated output bias voltages at output terminals (MIRN and MIRP).

Temperature and supply-voltage sensing circuit

The method of this invention prevents transient currents at high-frequency disable cycles and disables DC current paths after a minimum delay time, thereby reducing power dissipation. This invention includes a delay circuit functioning to prevent disablement of DC paths where chip-disable times occur at intervals below a minimum duration. The result is a decrease in the number of undesired voltage drops on internal power buses due to transient currents. The method detects external chip-disable pulses that occur before a minimum time duration, then prevents those pulses from powering down internal direct-current paths. At the same time, the output driver high impedance functionality of the chip-disable signal is preserved.

Memory device performance by delayed power-down

Low-voltage-correcting bias circuitry for a sense amplifier includes first, second and third N-channel transistors. The channel of the first transistor couples a current mirror to the input terminal of the amplifier and the gate of the second transistor, the channel of the second transistor couples the gate of the first transistor to a reference terminal. The channel of the third transistor couples the supply voltage to the gate of the first transistor. The gate of the third transistor is coupled to a reference voltage. A P-channel transistor has a channel coupling the supply voltage to the gate of the first transistor. The gate of the P-channel transistor is coupled to a low-voltage-sensing signal. Pre-charge circuitry includes a nonvolatile memory cell and fourth, fifth and sixth N-channel transistors. The channel of the fourth transistor is in series with the channel of the memory cell. The channel of the fifth transistor couples the channel of the memory cell to the input of the sense amplifier. The gates of the fourth and fifth transistors are coupled to a pre-charge operation control signal. The channel of the sixth transistor couples the supply voltage to the channel of the fourth transistor and the gate of the sixth transistor is coupled to the gate of the first transistor.

Sense amplifier with pre-charge circuit and low-voltage operation mode

The circuit of this invention improves significantly the programming speed of a Flash EPROM. The circuit includes a detector circuit (DC) using a pre-charge capacitor (C1), capacitor dividers [(C1/(C1+C2) and C3/(C2+C3)] and a voltage comparator (COMP) to signal a control logic circuit (CLC) when the programming voltage is within supply voltage (V.sub.cc) of its final value. At that point the control logic circuit (CLC) boosts the voltage on one terminal of a boost capacitor (BC) by the value of the supply voltage (V.sub.cc). The other terminal (XDD) of the boost capacitor (BC) furnishes the boosted programming voltage for the Flash EPROM.

Smart boost circuit for low voltage flash EPROM

A procedure for erasing a Flash EPROM array (AR) includes applying a series of erase pulses to all of the subarrays (S1, S2, etc.) of a Flash EPROM array (AR) simultaneously. Between each erase pulse, the memory cells (10) of each sub array (S1, S2, etc.) are simultaneously checked one row at a time and one column position at a time, to see whether or not any cell (10) is over-erased. If, at any time during the procedure a cell (10) is found to be over-erased, the over-erased condition is corrected and the erase procedure continues, but with erase pulses applied only to those subarrays (S1, S2, etc.) having non-erased memory cells (10) as in prior-art subarray erase procedures. Under almost all circumstances, the procedure of this invention decreases over-all erase time.

Erase procedure

A method for erasing blocks of a non-volatile memory includes detecting whether a block is in at least one of an erased state or a state secured from erasure; then setting a flag register at a first level for each block detected to be in at least one of an erased state or a state secured from erasure or at a second level for each block not so detected; then selecting for erasure blocks that have their respective flags set at the second level; and then erasing the selected blocks.

Smart erase algorithm with secure scheme for flash EPROMs

The power-on-reset test circuit of this invention includes two imbalanced latches to detect the occurrence of a transient power-on-reset signal. The occurrence of a transient power-on-reset signal is latched for later verification during circuit testing. Both latches are designed to default to a low voltage output (Vss) on initial power-up. One of the latches is set by the power-on-reset signal to a high-voltage output (Vcc) state. The other latch is set by a reference-potential input to a low-voltage output state. If the set latch has a high-voltage output and the other latch has a low-voltage output, then the power-on-reset circuitry is functioning properly.

Circuit for testing power-on-reset circuitry

A level shifter circuit 150 for selecting different voltage levels for programming memory cells 10 is provided. The level shifter 150 has an input 152 connected to a control circuitry and an output 154 connected to memory cells 10. The level shifter 150 is connected to two voltage sources: a high voltage source 166 and a low voltage source 164. The level shifter 150 has an isolation transistor 156 to buffer the input control circuitry from the higher voltage in the level shifter 150. Depending on the input control signal, either a first switching transistor 158 will select the low voltage source 164 for output or a second switching transistor 162 will select the high voltage source 166 for output. A pull-up transistor 162 is used to maintain the state of the switching transistors 158, 160 when the voltage sources 164, 166 ramp up. A voltage limiting transistor 170 reduces the voltage potential (breakdown voltage) across the drain and source terminals of the pull-up transistor 162.

Level shifter circuit

An array source signal discharge controller device (10) includes a pulse converter circuit (12) that receives an erase pulse signal (ERPULSE). The pulse converter circuit (12) converts the erase pulse signal (ERPULSE) into a pulse control signal (ERPCL) that is subsequently translated into a higher voltage level bias signal (ECL.sub.--). The higher voltage level bias signal (ECL.sub.--) drives array source signal generator circuits (16) that produce array source signals (AS) to erase particular array subsections of memory as determined by a selection circuit (17). The array source signal generator circuits (16) also generate array source command signals (ASCOM.sub.--) to indicate a discharging status of all array source signals (AS). An erase completion detector circuit (18) monitors the array source command signals (ASCOM.sub.--) and generates an array source detect signal (ASDET) to indicate completion of array source signal (AS) discharging. The pulse converter circuit (12) receives the array source detect signal (ASDET) and generates an erase completion signal (ERCTR) and a pulldown control signal ERCTR.sub.-- to control final discharge of the array source signals (AS) and indicate that normal memory access may resume. The pulse converter circuit (12) also generates a pulldown signal (ERD.sub.--) that controls discharge of the array source signals (AS) by preventing current surges from appearing on the array source signals (AS) during discharge.

Method and device for detecting and controlling an array source signal

A system for erasing a memory array in a memory has a supply voltage and a negative charge pump. The negative charge pump system includes (a) circuitry to select a memory array to be erased; (b) for circuitry to switch on the supply voltage Vnn for the charge pump; (c) circuitry to pump the supply voltage Vnn with the charge pump to produce a pumped negative voltage; (d) circuitry to erase the selected array with the pumped negative voltage; (e) circuitry to provide the pumping; and (f) circuitry to provide a discharge path for voltages trapped in the charge pump.

High voltage negative charge pump with low voltage CMOS transistors

The CMOS high-voltage sensor circuit has a voltage reference including, for example, of four N-channel MOS transistors; one pass-gate P-channel transistor; one current-mirror P-channel MOS transistor; and a conventional high-voltage sensor including, for example, of two P-channel MOS transistors and one N-channel MOS transistor. The sensor circuit of this invention generates a high-voltage signal at the output if the input voltage is greater than both the reference voltage plus two P-channel threshold voltages and the supply voltage Vcc plus two P-channel threshold voltages. The power-up or power-down sequence may be in any order without adversely affecting the operation of the circuit of this invention.

High-voltage sensor for integrated circuits

The power-on reset circuit of this invention includes a current-sensing circuit, a pulse-stretching circuit, and a voltage-reference circuit. The voltage-reference circuit consists, for example, of one N-Channel and one P-Channel MOS transistor. The circuit of this invention uses a static voltage reference comprised of CMOS transistors to detect the power-up condition. The circuit of this invention improves detection of a transient power-supply voltage Vcc loss and detects that power-supply voltage transient on both rising and falling edges.

Current-sensing power-on reset circuit for integrated circuits

The column-line short detection circuit of this invention includes a special test circuit that turns off wordlines (15), a N-channel transistor (23) for each column line (18), a decoder (19a) that uses only the least significant column address (20d) for input to the test circuit, and a sensor (SA) to detect current between shorted column lines (18). Because the column-line short detection circuit of this invention uses only the least significant address as input for column decoder (19a), it requires a very small number of transistors.

Circuit and method for detecting column-line shorts in

An improved negative charge pump system for erasing a memory array in a memory which has a supply voltage and a negative charge pump. The negative charge pump system includes (a) a device for selecting a memory array to be erased; (b) a device for switching on the supply voltage Vnn for the charge pump; (c) a device for pumping the supply voltage Vnn with the charge pump to produce a pumped negative voltage; (d) a device for erasing the selected array with the pumped negative voltage; (e) a device for stopping the pumping; and (f) a device for providing a discharge path for voltages trapped in the charge pump.

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Sugar Land, TX, United States of America

Tim M Coffman