Method for reading phase change memory cells having a clamping circuit
View Patent ↗A read circuit for reading at least one memory cell adapted to storing a logic value, the at least one memory cell including: a storage element made of a phase-change material; and an access element for coupling the storage element to the read circuit in response to a selection of the memory cell, the read circuit including: a sense current supply arrangement for supplying a sense current to the at least one memory cell; and at least one sense amplifier for determining the logic value stored in the memory cell on the basis of a voltage developing thereacross, the at least one sense amplifier comprising a voltage limiting circuit for limiting the voltage across the memory cell for preserving the stored logic value, wherein the voltage limiting circuit includes a current sinker for sinking a clamping current, which is subtracted from the sense current and depends on the stored logic value.
1. A method comprising:
supplying a sense current to a selected memory cell including a memory element having a stored logic value;
preventing the voltage across the selected memory cell from exceeding a clamping voltage;
diverting the sense current from said selected memory cell; and
using said diverted sense current to sense the state of the selected memory cell.
2. The method of claim 1 including limiting the voltage across the selected memory cell to below a predetermined clamping voltage lower than a threshold voltage.
3. The method of claim 2 including generating a current sinker control voltage based on the clamping voltage.
4. The method of claim 3 including using a voltage generator to generate a current sinker control signal in the form of a control voltage.
5. The method of claim 4 including using a transistor having a control terminal operatively connected to the current sinker control signal and a current delivery terminal coupled to the selected memory cell to generate a current sinker.
6. The method of claim 5 including receiving a clamping current to generate, by conversion of the clamping current, a measuring voltage corresponding to the resistance of the memory element.
7. The method of claim 1 including switching an access element from a non-thresholded condition to a thresholded condition such that, in the non-thresholded condition, the access element decouples the memory element from a read circuit and in the thresholded condition the access element couples the memory element to the read circuit.