Sensing amplifier to detect the memory cell current transition
First Claim
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1. An apparatus comprising:
- a memory cell;
a bit line connected to the memory cell;
a sensing voltage node connected to the bit line;
a comparator having a first input connected to the sensing voltage node and a second input connected to a reference voltage, the comparator circuit configured to;
compare a voltage at the sensing voltage node to the reference voltage; and
output a detection signal based on the comparison of the voltage at the sensing voltage node to the reference voltage;
a reference current source connected to the sensing voltage node and configured to provide a reference current to the sensing voltage node;
a supplemental current transistor connected to the sensing voltage node and configured to provide a supplemental current to the sensing voltage node in response to a current through the memory cell exceeding the reference current, the reference current source connected in parallel to the supplemental current transistor; and
a current limiter circuit connected to the reference current source and the supplemental current transistor, wherein the reference current source and the supplemental current transistor are connected in parallel between the current limiter circuit and the sensing voltage node.
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Abstract
This disclosure provides a method and apparatus for detecting a transition of a memory cell current from a first state to a second state. An example apparatus includes a memory cell, a supplemental current source, a comparator, a reference voltage and a reference current source in a configuration that allows for real time detection of the transition of a memory cell. Detection of a memory cell current transition is captured when the output of the comparator transitions from one state to a second state in response to a sensing voltage exceeding the reference voltage.
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Citations
19 Claims
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1. An apparatus comprising:
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a memory cell; a bit line connected to the memory cell; a sensing voltage node connected to the bit line; a comparator having a first input connected to the sensing voltage node and a second input connected to a reference voltage, the comparator circuit configured to; compare a voltage at the sensing voltage node to the reference voltage; and output a detection signal based on the comparison of the voltage at the sensing voltage node to the reference voltage; a reference current source connected to the sensing voltage node and configured to provide a reference current to the sensing voltage node; a supplemental current transistor connected to the sensing voltage node and configured to provide a supplemental current to the sensing voltage node in response to a current through the memory cell exceeding the reference current, the reference current source connected in parallel to the supplemental current transistor; and a current limiter circuit connected to the reference current source and the supplemental current transistor, wherein the reference current source and the supplemental current transistor are connected in parallel between the current limiter circuit and the sensing voltage node. - View Dependent Claims (2, 3, 4, 5, 6, 7, 9, 10)
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8. An apparatus comprising:
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a memory cell; a bit line connected to the memory cell; a sensing voltage node connected to the bit line; a comparator having a first input connected to the sensing voltage node and a second input connected to a reference voltage, the comparator circuit configured to; compare a voltage at the sensing voltage node to the reference voltage; and output a detection signal based on the comparison of the voltage at the sensing voltage node to the reference voltage; a reference current source connected to the sensing voltage node and configured to provide a reference current to the sensing voltage node; a supplemental current transistor connected to the sensing voltage node and configured to provide a supplemental current to the sensing voltage node in response to a current through the memory cell exceeding the reference current, the reference current source connected in parallel to the supplemental current transistor; and a source-follower circuit connected to the bit line and the sensing voltage node, wherein the source follower circuit is configured to maintain a fixed voltage on the bit line, and wherein the source-follower circuit comprises; an operational amplifier having a positive input, a negative input, and an output; and a first transistor having a gate connected to the output of the operational amplifier, wherein the first transistor further comprises a drain connected to the sensing voltage node and a source connected to the memory cell via the bit line.
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11. A method comprising:
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applying a reference current to a bit line associated with a memory cell; during a first current state of the memory cell, activating a supplemental current transistor to provide supplemental current to the bit line associated with the memory cell; detecting a transition of the memory cell from the first current state to a second current state in response to an amount of current on the bit line falling below a level of the reference current, wherein the amount of current on the bit line falling below the amount of the reference current causes the supplemental current transistor to deactivate and further causes a sensing voltage received at a comparator to exceed a reference voltage; and limiting a maximum current on the bit line using a current limiter circuit, wherein the current limiter circuit comprises a limit current source and a current mirror connected to both the supplemental current transistor and a source of the reference current. - View Dependent Claims (12, 13, 14, 15)
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16. An apparatus comprising:
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means for applying a reference current to a bit line associated with a memory cell; means for selectively providing supplemental current to the bit line associated with the memory cell, wherein the means for selectively providing supplemental current further comprises means for deactivating the supplemental current in response to an amount of current on the bit line exceeding an amount of the reference current; means for detecting a transition of the memory cell from a first current state to a second current state in response to a sensing voltage exceeding a reference voltage, wherein the sensing voltage is dependent on the amount of current on the bit line; and means for limiting a maximum current on the bit line, wherein the means for limiting comprises a limit current source and a current mirror connected to both the means for selectively providing supplemental current and the means for applying the reference current.
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17. A method comprising:
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programming a memory cell, wherein programming the memory cell comprises transitioning the memory cell from a first state to a second state; performing an operation to determine whether the memory cell is in the first state or the second state, wherein performing the operation comprises comparing a sensing voltage at a sensing voltage node to a reference voltage, wherein the sensing voltage is based on a first current received at the sensing voltage node from a supplemental current transistor and a second current received at the sensing voltage node from a reference current source, and wherein a combination of the first current and the second current is limited by a current limiter circuit, wherein the current limiter circuit comprises a limit current source and a current mirror connected to both the supplemental current transistor and a source of the reference current. - View Dependent Claims (18, 19)
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Specification