Overdrive Feedback Control for RC Network Voltage Transition
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Solution Overview
Problem
RC delay during charging and discharging limits signal propagation speed in large integrated circuits, such as memory arrays, due to the dominant RC time constant, which hinders performance improvement as circuit size and complexity increase.
Innovation Solution
A circuit and method utilizing a feedback control scheme with overdrive techniques, where a driver circuit connects to a load through switches, using a resistance in series with a second switch to monitor and control voltage transitions, allowing accurate feedback to stop the overdrive when the target voltage is reached, thereby reducing delay and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional RC charging/discharging is used to supply voltage levels, then the circuit structure remains simple, but the transition time is excessively long due to dominant RC delay
Solution Approach 1:
The voltage transition process is segmented into multiple phases: initial overdrive phase (first switch closed, second switch open) and correction phase (first switch open, second switch closed). This segmentation allows the circuit to first rapidly charge/discharge the capacitive load beyond the target voltage, then gradually correct to the precise target level, thereby resolving the contradiction between fast transition speed and accurate voltage control.
Solution Approach 2:
The first switch is closed preliminarily to establish a low-impedance path for rapid voltage transition during the overdrive phase. This preliminary action enables the capacitive load to be charged or discharged quickly beyond the target voltage level before the correction phase begins, significantly reducing the overall transition time while maintaining simplicity.
2Loss of time
If overdrive technique is applied to reduce RC delay, then transition speed improves, but power consumption increases due to excessive voltage swing
Solution Approach 1:
A feedback mechanism using a second comparator continuously monitors the voltage at the intermediate node and controls the switching of the first and second switches. When the voltage reaches the target level, the feedback signal stops the overdrive action by opening the first switch and closing the second switch. This feedback control precisely terminates the overdrive phase, preventing excessive voltage swing and reducing unnecessary power consumption while maintaining fast transition speed.
Solution Approach 2:
The circuit applies partial overdrive by using the second switch to provide a controlled leakage path during the correction phase. This partial action allows the voltage to be gradually corrected from the overdrive level back to the target level without requiring full overdrive throughout the entire transition, thereby reducing power consumption while still achieving fast initial response.
3Measurement precision
If simple switch control is used without feedback, then the circuit remains simple, but voltage accuracy is poor due to inability to stop overdrive at precise target level
Solution Approach 1:
The second comparator and associated control logic form a feedback loop that continuously monitors the voltage at the intermediate node and adjusts the switching states accordingly. This feedback mechanism provides precise voltage level detection and control, enabling the circuit to accurately stop the overdrive action exactly when the target voltage is reached, thereby achieving high voltage accuracy without requiring complex external control circuits.
Solution Approach 2:
The second switch acts as an intermediary element between the voltage source and the capacitive load during the correction phase. It provides a controlled leakage path that allows gradual voltage adjustment from the overdrive level to the target level. This intermediary mechanism simplifies the control logic by providing automatic voltage regulation without requiring complex control circuits, while still achieving precise voltage accuracy.
Data Source
AI summary
Techniques are presented to improve the performance, accuracy and power consumption of on-chip voltage biasing and transmission for highly loaded RC networks (such as wordlines or bitlines in NAND or 3D memory arrays) that are otherwise limited by the physics of RC time constant. When transitioning the near-end voltage of the network, an under-drive or over-drive level is applied, combined with feedback control to estimate when the far-end voltage approaches the desired level.