ROM Keeper Transistor Dedicated Control Signal
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Solution Overview
Problem
Conventional ROM circuits face performance limitations due to over-discharging of bit lines caused by memory cell leakage, leading to unstable sensing windows and reduced signal quality, which is not adequately addressed by existing keeper circuits that either fail to stabilize voltage or complicate the sensing process.
Innovation Solution
A ROM memory circuit with a keeper transistor controlled by a dedicated control signal, where the transistor maintains the voltage of the electrical line at a desired level independent of its threshold voltage, allowing for stable voltage stabilization without interfering with the sensing process and occupying less space.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional keepers are used to counter leakage, then voltage stabilization is attempted, but the sensing process becomes complicated and the read window becomes unstable
Solution Approach 1:
The patent extracts the keeper function from the sensing process by using a dedicated control signal that is independent of the sense amplifier's operation. The keeper transistor is controlled separately through a dedicated control signal line, allowing voltage stabilization to occur without interfering with the sensing mechanism. This separation removes the complexity introduced by conventional feedback keepers that were coupled to the sensing process.
Solution Approach 2:
The patent segments the control functions by introducing a dedicated control signal line for the keeper transistor that is independent from the sense amplifier control. This segmentation allows the keeper to operate autonomously based on leakage conditions without being influenced by the sensing operation, thereby stabilizing voltage while keeping the sensing process simple and clean.
2Reliability
If feedback keepers are used to maintain voltage, then leakage is counteracted, but the keeper transistor turns off when voltage drops below threshold, causing dramatic voltage drops and unstable sensing windows
Solution Approach 1:
The patent applies preliminary action by controlling the keeper transistor to turn on before the voltage drop becomes problematic. The dedicated control signal is activated in advance to maintain the keeper transistor in the on-state, preventing the voltage from dropping below the threshold in the first place. This proactive approach ensures stable voltage throughout the sensing window without the dramatic drops that occur with reactive feedback keepers.
Solution Approach 2:
The patent uses feedback through the dedicated control signal that monitors the voltage level and adjusts the keeper transistor's operation accordingly. When voltage drops due to leakage, the control signal responds by maintaining or enhancing the keeper's conduction, creating a stable feedback loop that prevents voltage from dropping below the threshold and ensures consistent sensing window stability.
3Measurement precision
If bit lines are discharged to ground for reading 0, then digital data is sensed, but the bit line is always over-discharged due to memory cell leakage, limiting the signal swing value
Solution Approach 1:
The patent introduces the keeper transistor as a counterweight to the over-discharging effect of memory cell leakage. The keeper transistor provides a counter-current that opposes the leakage current, effectively balancing the discharge process. This counteraction allows the bit line to reach the proper discharge level for sensing without being over-discharged, thereby restoring the full signal swing value needed for accurate digital data reading.
Data Source
AI summary
A ROM memory circuit is disclosed having at least one electrical line, at least one keeper circuit electrically connected to the at least one electrical line, the keeper circuit including a first transistor, a terminal of the first transistor is driven by a dedicated control signal, wherein the dedicated control signal is configured to keep the voltage of the at least one electrical line at a first voltage.