OTP Memory Readout With Offset-Current Subtraction
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Solution Overview
Problem
The increase in circuit area and power consumption of clamp elements in semiconductor devices due to the use of OTP cells, and the complexity of timing control in readout operations for variable resistance-type storage elements, particularly in STT-MRAM, is a challenge.
Innovation Solution
Incorporating a bit line, first and second memory cells, a clamp element, a reference current source, a sense amplifier, and an offset current source to detect the magnitude relationship between reference and readout currents, thereby suppressing the increase in clamp element area and simplifying timing control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a clamp element is used to apply readout potential to OTP cells with very low resistance, then the cell current can be detected, but the circuit area and power consumption of the clamp element increase significantly
Solution Approach 1:
The clamp element is divided into multiple sub-clamp elements that operate in parallel. Each sub-clamp element handles a portion of the total current, allowing the overall clamp function to be achieved while reducing the area and power consumption of each individual clamp element. The control circuit selectively activates appropriate sub-clamp elements based on the cell type being read.
Solution Approach 2:
The clamp element configuration is made dynamic through selective activation. The control circuit determines whether to activate the full clamp element or only partial sub-clamp elements based on whether the read operation targets a normal memory cell or an OTP cell. This dynamic adaptation allows optimal current clamping with minimized area and power usage for each specific operation type.
2Reliability
If the clamp element is designed to handle the maximum cell current for OTP cells, then accurate readout is possible, but the power consumption and area increase for all readout operations including normal memory cells
Solution Approach 1:
The clamp element system transitions from a static, always-full-activation design to a dynamic, selective activation design. The control circuit monitors the readout operation type and activates only the necessary portion of the clamp element (full clamp for OTP cells, partial sub-clamps for normal cells), thereby maintaining readout accuracy while significantly reducing average power consumption.
Solution Approach 2:
The operational parameters of the clamp element (activation state, current handling capacity) are changed dynamically based on the readout requirements. By adjusting which sub-clamp elements are activated and modifying the effective clamp strength, the system adapts to different cell types, ensuring reliable detection while optimizing power efficiency for each operation mode.
3Adaptability or versatility
If separate readout circuits are designed for normal memory cells and OTP cells, then each cell type can be readout optimally, but the device complexity increases
Solution Approach 1:
A single readout circuit design is created that can handle both normal memory cells and OTP cells through the introduction of selectable sub-clamp elements. The circuit maintains universal applicability by allowing dynamic reconfiguration of the clamp element activation pattern, eliminating the need for separate dedicated readout circuits for each cell type while preserving optimal readout performance for both.
Solution Approach 2:
The clamp element is segmented into multiple independently controllable sub-clamp elements. This segmentation allows the control circuit to selectively activate appropriate portions of the clamp element based on the cell type being read, providing the adaptability of multiple specialized circuits while maintaining the simplicity of a single unified circuit architecture.
Data Source
AI summary
A clamp element 46 applies a fixed potential to a bit line BL at a time of a readout operation. A reference current source RCS generates a reference current Iref. An offset current source OCS1 is activated at a time of a readout operation for an OTP cell OTPC, and at a time of being activated, generates an offset current Iof1 to be subtracted from a cell current Icel. At the time of the readout operation for the OTP cell OTPC, the sense amplifier SA detects a magnitude relationship between the reference current Iref and a readout current Ird obtained by subtracting the offset current Iof1 from the cell current Icel.