Sense Amplifier Cross-Coupled Capacitors for Read Margin Stability
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Solution Overview
Problem
Sense amplifier circuits in memory circuits, such as MRAM, experience reduced read margin due to direct and indirect coupling between data and reference inputs, leading to incorrect data reading and reduced reliability.
Innovation Solution
The implementation of a sense amplifier design that minimizes direct coupling between data and reference inputs and reduces indirect coupling effects by using cross-coupled capacitors, specifically FEOL, MEOL, and BEOL capacitors, to maintain or improve the read margin without increasing the circuit layout area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If direct coupling between data input Q and reference input QB is implemented in sense amplifier circuits, then the circuit structure is simplified and area is reduced, but the read margin deteriorates and data reading reliability is reduced
Solution Approach 1:
The patent divides the sense amplifier circuit into separate direct-coupled pairs (first data input Q0 directly coupled to first reference input QB0, second data input Q1 directly coupled to second reference input QB1) rather than sharing a common reference input. This segmentation allows each pair to operate independently, maintaining the area benefits of direct coupling while preventing the read margin deterioration that occurs when multiple data inputs share a common reference input.
2Device complexity
If reference input QB is directly coupled to data input Q, then the circuit complexity is reduced, but the voltage level stability of reference input QB deteriorates
Solution Approach 1:
The patent segments the reference input into multiple independent reference inputs (QB0, QB1, etc.), each directly coupled to a corresponding data input. This segmentation isolates the voltage level stability issue to individual pairs, preventing the voltage instability that would occur if multiple data inputs were directly coupled to a single shared reference input.
3Reliability
If cross-coupled capacitors are added to reduce indirect coupling effects, then the read margin is improved, but the device complexity increases
Solution Approach 1:
The patent extracts and eliminates the indirect coupling paths through internal nodes by using direct coupling between corresponding data and reference inputs. This removes the need for additional cross-coupled capacitors that would be required to compensate for indirect coupling effects, thereby improving read margin without increasing device complexity.
4Ease of operation
If voltage levels on data input Q and reference input QB change during operation due to coupling, then the circuit operation is simplified, but the measurement precision of voltage level comparison deteriorates
Solution Approach 1:
The patent segments the voltage level comparison into independent pairs (Q0 with QB0, Q1 with QB1, etc.), where each pair maintains stable voltage levels during operation. This segmentation prevents the voltage level instability that would occur in a shared reference configuration, thereby maintaining measurement precision while keeping the operation simple.
Data Source
AI summary
A sense amplifier including a first input transistor having a first input gate and a first drain/source terminal, a second input transistor having a second input gate and a second drain/source terminal, a latch circuit, and a first capacitor. The latch circuit includes a first latch transistor having a third drain/source terminal connected to the first drain/source terminal and a second latch transistor having a fourth drain/source terminal connected to the second drain/source terminal. The first capacitor is connected on one side to the first input gate and on another side to the fourth drain/source terminal to reduce a coupling effect in the sense amplifier.