Memory Device Leakage Compensation via PTAT and CTAT Current Subtraction
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Solution Overview
Problem
Conventional semiconductor memory devices face difficulties in effectively compensating for bit line leakage current, which exponentially increases with temperature due to the limitations of proportional to absolute temperature (PTAT) current compensation methods.
Innovation Solution
A memory device and control method that generate a third current by subtracting a complementary to absolute temperature (CTAT) current from a PTAT current, and use this third current to control the load current supplied to the bit line, along with a pre-charge pulse signal, to efficiently compensate for bit line leakage current across varying temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a PTAT current compensation method is used, then the compensation circuit can provide temperature-proportional current, but it cannot effectively compensate for bit line leakage current that exponentially increases with temperature
Solution Approach 1:
The compensation current is segmented into two distinct components: a PTAT current component that increases with temperature and a CTAT current component that decreases with temperature. These two components are generated separately and then combined to form the total compensation current, allowing independent optimization of each component's temperature characteristic
Solution Approach 2:
The invention changes the temperature dependency parameter of the compensation current by combining two currents with opposite temperature coefficients. The PTAT current has a positive temperature coefficient while the CTAT current has a negative temperature coefficient, and their combination creates a compensation current that can effectively counteract the exponentially increasing bit line leakage current across a wide temperature range
2Reliability
If the bit line leakage current is compensated using conventional methods, then some temperature compensation is achieved, but the exponential increase of leakage current with temperature cannot be effectively addressed
Solution Approach 1:
The CTAT current acts as a counterweight to the PTAT current, providing an opposing temperature dependency that balances the overall compensation current. This counterbalancing approach allows the system to counteract the exponential increase in bit line leakage current by adjusting the relative weights of the two current components based on temperature conditions
3Device complexity
If a simple PTAT current source is used for compensation, then the circuit complexity is low, but the compensation precision for exponentially increasing leakage current is insufficient
Solution Approach 1:
The compensation current is formed as a composite of two different current types with complementary temperature characteristics. The PTAT and CTAT currents are combined in a current addition circuit to create a composite compensation current that leverages the strengths of both current types to achieve high precision compensation across varying temperatures
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces bit line leakage current and improves read speed by adjusting the magnitude and width of the pre-charge pulse signal based on temperature changes, ensuring stable compensation against temperature variations.
Implementation Method 1
a first current generator that generates a first current having a proportional to absolute temperature (PTAT) characteristic, based on the at least one current control code from the controller
Implementation Method 2
a second current generator that generates a second current having a complementary to absolute temperature (CTAT) characteristic, based on the current control code from the controller
Implementation Method 3
a subtractor configured to generate a third current by subtracting the second current from the first current
Implementation Method 4
a sense amplifier configured to control, based on the third current, a load current to be supplied to the bit line, and generate a bit line compensation current for compensating for a leakage current of the bit line
Data Source
AI summary
Disclosed is a memory device, which includes a memory cell, a bit line connected to the memory cell, a controller that generates at least one current control code, a first current generator that generates a first current having a proportional to absolute temperature (PTAT) characteristic, based on the at least one current control code from the controller, a second current generator that generates a second current having a complementary to absolute temperature (CTAT) characteristic, based on the at least one current control code from the controller, a subtractor that generates a third current by subtracting the second current from the first current, and a sense amplifier that controls a load current to be supplied to the bit line based on the third current, and generates a bit line compensation current for compensating for a leakage current of the bit line.