Constant-Current Oscillator Circuit for Stable DRAM Refresh Timing
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Solution Overview
Problem
Oscillator circuits in DRAMs face variations in refresh cycle due to threshold voltage and temperature changes, leading to increased current consumption and test complexity, necessitating a solution to generate a stable oscillating signal unaffected by these variations.
Innovation Solution
An oscillator circuit with two constant current sources and a control circuit that adjusts the voltage range to operate above the threshold voltage of the MOS capacitor, ensuring the oscillating cycle is not affected by capacitance variations, and allows for adjustable cycle measurement using a tester.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the refresh cycle is prolonged to reduce current consumption, then current consumption decreases, but the refresh cycle variation increases making it difficult to ensure reliable operation
Solution Approach 1:
The patent changes the operating voltage range parameter to be above the threshold voltage, which stabilizes the capacitance value and reduces refresh cycle variation. This allows for a longer refresh cycle with reduced current consumption while maintaining reliability through the stabilized capacitance characteristic.
2Quantity of substance
If the memory capacity is increased to improve storage capability, then storage capability improves, but the current consumption during refresh operations increases
Solution Approach 1:
By changing the voltage operating range to be above threshold voltage, the capacitance becomes more stable and less sensitive to variations. This reduces the refresh cycle variation, allowing for more efficient refresh operations and lower current consumption even in high-capacity memory devices.
3Reliability
If the refresh cycle is set with a margin to account for variation, then reliability improves, but current consumption increases due to shorter cycle
Solution Approach 1:
The patent changes the voltage operating range to above threshold voltage, which inherently stabilizes the capacitance and reduces refresh cycle variation. This allows for setting the refresh cycle closer to the theoretical limit without requiring excessive margin, thereby reducing current consumption while maintaining reliability.
4Device complexity
If conventional oscillator circuits are used, then the circuit complexity is low, but the oscillating cycle varies due to threshold voltage and temperature changes
Solution Approach 1:
The patent changes the voltage operating range parameter to be above threshold voltage, which stabilizes the capacitance characteristic. This simple parameter change stabilizes the oscillating cycle without requiring complex circuit modifications, maintaining low circuit complexity while improving stability.
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 stabilizes the oscillating cycle, reducing current consumption and test complexity by maintaining the oscillating cycle within a predetermined range, unaffected by threshold voltage and temperature variations, thus enhancing the efficiency and reliability of the DRAM refresh operation.
Implementation Method 1
a capacitor (35), a first constant current source (33), a second constant current source (34)
Implementation Method 2
a comparator (31), a comparator (32) to switch, in response to a comparison of a potential at the end of the capacitor with the first and second reference potentials
Data Source
AI summary
An oscillator circuit includes a capacitor, a first constant current source electrically couplable to an end of the capacitor, a second constant current source electrically couplable to the end of the capacitor, a control circuit coupled to the end of the capacitor, a first reference potential, and a second reference potential to switch, in response to a comparison of a potential at the end of the capacitor with the first and second reference potentials, between a first operation to charge the capacitor by electrically coupling the first constant current source to the end of the capacitor and a second operation to discharge the capacitor by electrically coupling the second constant current source to the end of the capacitor, and a circuit configured to have an output signal thereof exhibiting a signal transition in response to timing at which the switching occurs between the first operation and the second operation.