Dual-Stage MRAM Sensing Circuit for Offset Cancellation
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Solution Overview
Problem
As MRAM technology scales, the critical switching current for writing decreases, leading to reduced sensing margin and increased risk of read disturbance due to process variations, which affects the reliability and speed of data reading in magnetic random access memory (MRAM) devices.
Innovation Solution
An offset canceling dual stage sensing circuit and voltage sense amplifier are introduced, which improve tolerance to fabrication process variations and reduce read disturbance by generating adjustable load PMOS gate voltages and using equalization transistors to cancel out offset voltages, thereby increasing the sensing margin and speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the critical switching current for writing decreases with technology scaling, then the writing capability is improved, but the sensing margin is reduced and read disturbance risk increases
Solution Approach 1:
The sensing circuit performs preliminary offset voltage measurement and cancellation before the actual read operation. The circuit applies a first sensing current to measure offset voltage, then applies a second sensing current in the opposite direction to cancel the offset, preparing the circuit for accurate subsequent read operations with reduced disturbance risk
Solution Approach 2:
The sensing circuit uses feedback mechanisms to dynamically adjust sensing currents based on measured offset voltages. The circuit monitors the voltage developed across the MTJ and adjusts the sensing current magnitude and direction to compensate for process variations and minimize read disturbance
2Reliability
If the sensing current is reduced to prevent read disturbance, then the reliability is improved, but the sensing speed decreases
Solution Approach 1:
The sensing circuit employs periodic action by applying sensing currents in alternating directions (first direction, then second opposite direction) to measure and cancel offset voltages. This periodic current reversal enables the circuit to distinguish between offset voltage and actual signal voltage, allowing higher sensing currents to be used without causing read disturbance
Solution Approach 2:
The circuit dynamically changes the parameter of sensing current magnitude and direction based on the measured offset voltage. By adjusting the sensing current parameters adaptively, the circuit can operate at higher currents for faster sensing while compensating for offset effects to prevent read disturbance
3Device complexity
If process variations are not compensated, then the device complexity is reduced, but the measurement precision deteriorates
Solution Approach 1:
The sensing circuit performs self-service by automatically measuring and canceling its own offset voltages without requiring external calibration or complex compensation circuits. The circuit uses its own sensing current paths and measurement capabilities to identify and eliminate offset errors, achieving high measurement precision through self-compensation
Data Source
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AI summary
An offset canceling dual stage sensing method includes sensing a data value of a resistive memory data cell using a first load PMOS gate voltage generated by a reference value of a resistive memory reference cell in a first stage operation. The method also includes sensing the reference value of the resistive memory reference cell using a second load PMOS gate voltage generated by the data value of the resistive memory data cell in a second stage operation of the resistive memory sensing circuit. By adjusting the operating point of the reference cell sensing, an offset canceling dual stage sensing circuit increases the sense margin significantly compared to that of a conventional sensing circuit.