Reference-Free Multi-Level Sensing Circuit for Computing-in-Memory
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Solution Overview
Problem
Conventional computing-in-memory applications require a reference generator to generate multiple reference voltages, leading to high power consumption due to a small sensing margin between bit-line voltage levels and reference voltages.
Innovation Solution
A reference-free multi-level sensing circuit utilizing a voltage sense amplifier, precharging unit, and encoding unit, which includes registers and an encoder to estimate voltage levels of bit lines without a reference generator, employing a differential multi-level sensing scheme to increase sensing margin and eliminate power consumption associated with the reference generator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a reference generator is used to generate multiple reference voltages for sensing, then the sensing capability is improved, but the power consumption increases significantly
Solution Approach 1:
The reference generator component is completely removed from the sensing circuit. Instead of generating multiple reference voltages, the patent uses a differential sensing approach where two bit lines are sensed simultaneously without external reference voltages, extracting only the essential sensing function while eliminating the power-consuming reference generation subsystem.
Solution Approach 2:
The sensing circuit uses the bit lines themselves as the sensing elements. The voltage levels on the bit lines directly represent the computational results, and the differential sensing amplifier compares these voltages directly without needing external reference voltages. The system serves itself by using the signal lines as both data carriers and sensing elements.
2Measurement precision
If multiple reference voltages are generated to handle various input patterns, then the measurement accuracy is improved, but the device complexity increases
Solution Approach 1:
The reference generator subsystem is extracted and removed entirely. The patent simplifies the sensing circuit by eliminating the complex reference voltage generation network, keeping only the essential differential sensing amplifier and register components needed for accurate multi-level sensing.
Solution Approach 2:
The differential sensing amplifier serves multiple functions: it compares voltage levels, determines computational results, and works with various input patterns simultaneously. The same circuit structure handles all sensing operations without needing separate reference voltage generation circuits for different input conditions.
3Reliability
If a reference generator is used to sense bit line voltage levels, then the sensing margin is improved, but the power consumption increases
Solution Approach 1:
The bit lines serve dual purposes as both data transmission channels and sensing elements. The voltage levels on the bit lines directly indicate the computational results, and the differential amplifier uses these same lines to perform sensing without requiring separate reference voltage sources, achieving both reliability and low power consumption.
Solution Approach 2:
The differential sensing approach creates a balanced sensing structure where two bit lines are compared symmetrically. This equipotential approach ensures that the sensing margin is determined by the voltage difference between bit lines rather than by reference voltage stability, reducing power consumption while maintaining reliable sensing.
Data Source
AI summary
A reference-free multi-level sensing circuit for computing-in-memory applications is controlled by a first bit line and a second bit line. An encoding unit generates a first register output value and a plurality of encoded values. The first register output value feedback controls a precharging unit so as to enable the precharging unit to precharge one of the first bit line and the second bit line according to the first register output value. A voltage level of the one of the first bit line and the second bit line is lower than a voltage level of the other one of the first bit line and the second bit line. The encoded values and the first register output value are formed a multi-bit signal to estimate voltage levels of the first bit line and the second bit line.