Offset compensated sensing for magnetic random access memory
View Patent ↗An offset compensated memory element voltage supply including a differential amplifier with a compensation circuit, and a transistor with a gate connected to the output of the differential amplifier. The compensation circuit of the differential amplifier includes a compensation capacitor that stores a compensation voltage during a calibration phase, and applies the stored compensation voltage to a compensation input of the compensation circuit of the amplifier during a measurement phase. Feedback from a source of the transistor controls the output of the differential amplifier to maintain a standard voltage across a resistive memory element connected to the source during measurement of the resistance of the resistive memory element, and the compensation circuit improves the accuracy of the voltage across the resistive memory element by compensating for an offset voltage of the differential amplifier.
1. A voltage source for a resistive memory device, the resistive memory device having a plurality of row lines and resistive memory elements, the voltage source comprising:
a pull-up voltage circuit for maintaining at least one row line at a predetermined array voltage, the pull-up voltage circuit comprising:
a first differential amplifier operatively connected to a reference voltage; and
a second differential amplifier operatively connected to a compensation voltage and an output of the first differential amplifier.
2. The voltage source of claim 1 , wherein the first differential amplifier comprises:
a pull-up resistor electrically connected to a supply voltage;
an output connected to the resistor;
an inverting transistor connected to the output and controlled by an inverting input;
a non-inverting transistor connected to the supply voltage and controlled by a non- inverting input;
a first current source connected between the inverting and non-inverting transistors and ground; and
an offset voltage source connected to a gate of the non-inverting transistor. transistor.
3. The voltage source of claim 2 , wherein the second differential amplifier comprises:
a first compensation transistor connected to the inverting transistor and the output of the first differential amplifier;
a second compensation transistor connected to the non-inverting transistor;
a second current source connected between the compensation transistors and ground;
a first compensation capacitor connected to a gate of the first compensation transistor; and
a second compensation capacitor connected to a gate of the second compensation transistor.
4. A compensated differential amplifier device comprising:
a first differential amplifier comprising:
a pull-up resistor electrically connected to a supply voltage;
an output electrically connected to the resistor;
an inverting transistor, the inverting transistor comprising:
a gate connected to an inverting input;
a first source/drain region electrically connected to the output; and
a second source/drain region;
a non-inverting transistor comprising:
a gate connected to a non-inverting input;
a first source/drain region electrically connected to the supply voltage; and
a second source/drain region;
a first current source comprising:
a first terminal connected to the second source/drain region of the inverting transistor and the second source/drain connection of the non- inverting transistor; and
a second terminal connected to ground; and
an offset voltage source connected to the gate of the non-inverting transistor; and
a second differential amplifier comprising:
a first compensation transistor comprising:
a first source/drain region electrically connected to the first source/drain region of the inverting transistor and to the output of the first differential amplifier;
a second source/drain region; and
agate;
a second compensation transistor comprising:
a first source/drain region electrically connected to the first source/drain region of the non-inverting transistor;
a second source/drain region; and
a gate;
a second current source comprising:
a first terminal connected to the second source/drain region of the inverting transistor and the second source/drain connection of the non- inverting transistor; and
a second terminal connected to ground; and
a first compensation capacitor comprising:
a first terminal electrically connected to the gate of the first compensation transistor; and
a second terminal connected to ground; and
a second compensation capacitor comprising:
a first terminal electrically connected to the gate of the second compensation transistor; and
a second terminal connected to ground.
5. The compensated differential amplifier device of claim 4 , wherein a second source/drain region of the non-inverting transistor is connected to a complementary output.
6. A control circuit for controlling an amplifier in a resistive memory device, the control circuit comprising:
a first phase output operatively connected to a first plurality of switches; and
a second phase output operatively connected to a second plurality of switches,
wherein the control circuit is operable to alternate between a calibration mode configuration and a resistive element measurement mode configuration.
7. The control circuit of claim 6 , wherein the control circuit is operable to place the amplifier in the calibration mode at the beginning of each read cycle.
8. The control circuit of claim 6 , wherein the control circuit is operable to place the amplifier in the calibration mode prior to a first read, and then operable to return the amplifier to the calibration mode only after a predefined number of read cycles.
9. The control circuit of claim 6 , wherein the control circuit is operable to place the amplifier in the calibration mode prior to a first read cycle, and then operable to return the amplifier to the calibration mode only after a definite value of voltage offset is sensed on an output.