Memory sensing circuit and method for low voltage operation
AssigneeSanDisk Corporation
InventorRaul-Adrian Cernea
Life of this patent
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Abstract
A sensing module operates with a sense amplifier sensing a conduction current of a memory cell via a coupled bit line under constant voltage condition in order to minimize bit-line to bit-line coupling. The rate of discharge of a dedicated capacitor as measured by a change in the voltage drop there across in a predetermined period is used to indicate the magnitude of the conduction current. The voltage cannot drop below a minimum level imposed by a circuit for maintaining the constant voltage condition on the bit line. A voltage shifter is used to boost the voltage during the discharge and to unboost the voltage after the discharge, so that the change in voltage drop properly reflects the rate of discharge without running into the minimum level.
Claims36
A method of sensing a conduction current of a memory cell comprising:
- (a) providing a voltage supply;
- (b) coupling a capacitor to said memory cell via an intermediate circuit;
- (c) charging said capacitor to an initial voltage above a reference voltage by coupling to said voltage supply;
- (d) decoupling said capacitor from said voltage supply;
- (e) boosting the voltage on the capacitor by a predetermined amount after said decoupling;
- (f) discharging said capacitor with said conduction current of said memory cell for a predetermined period of time such that said voltage on the capacitor decreases to a discharged voltage;
- (g) decoupling said capacitor from the intermediate circuit;
- (h) reducing said discharged voltage on the capacitor by said predetermined amount;
- and
- (i) comparing the voltage on the capacitor with the reference voltage to give a measure of said conduction current.
A sensing circuit for sensing a conduction current of a memory cell, comprising:
- a capacitor;
- a voltage supply
- a precharge circuit powered by said voltage supply and coupleable to said capacitor;
- a voltage shifter able to shift the voltage on said capacitor;
- an intermediate circuit able to couple said capacitor to said memory cell;
- a first control signal to enable said precharge circuit to couple to said capacitor to charge said capacitor to an initial voltage above a reference voltage;
- a second control signal to decouple said precharge circuit from said capacitor;
- a third control signal to enable said voltage shifter to boost the voltage on said capacitor by a predetermined amount;
- said intermediate circuit coupling said capacitor to discharge through said conduction current of said memory cell such that the voltage on said capacitor decreases to a boosted discharged voltage after a predetermined period of time;
- a fourth control signal to decouple said capacitor from said intermediate circuit after the predetermined period of time;
- a fifth control signal to disable said voltage shifter such that the boosted discharged voltage is reduced by said predetermined amount to a final discharged voltage;
- and
- a voltage comparator to compare the final discharged voltage with a reference voltage to give a measure of said conduction current of said memory.
A sensing circuit for sensing a conduction current of a memory cell, comprising:
- a capacitor;
- a voltage supply;
- means for charging said capacitor to an initial voltage above a reference voltage using said voltage supply;
- an intermediate circuit able to couple said capacitor to said memory cell;
- means for couple said capacitor to said intermediate circuit to discharge said capacitor with said conduction current of said memory cell for a predetermined period of time such that the voltage on said capacitor decreases to a discharged voltage;
- means for boosting the voltage on said capacitor by a predetermined amount;
- means for decoupling said capacitor from the intermediate circuit after the predetermined period of time;
- means for reducing the discharged voltage by said predetermined amount;
- and
- a voltage comparator for comparing the voltage on said capacitor with the reference voltage to give a measure of said conduction current of said memory cell.
A method of sensing a conduction current of a memory cell comprising:
- charging a capacitor to a voltage initially at a first level;
- discharging the capacitor with said conduction current so that the voltage discharges from the first level;
- boosting the voltage by a predetermined amount;
- terminating discharging the capacitor after a predetermined period of time;
- reducing the voltage by the predetermined amount to a final level;
- and
- comparing the final level with a reference voltage level to give a measure of said conduction current.
Dependencies are inferred from the claim text.