Sense-Amplifier POR Circuit for Sharp Reset Threshold Detection
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Solution Overview
Problem
Existing Power-On Reset (POR) circuits fail to meet modern requirements for precision turn-on voltage, wide VDD ramping rate, zero standby, and low transient current, and are impractical due to large area and complex analog circuits.
Innovation Solution
A POR circuit based on a high-gain sense amplifier (SA) bias circuit, coupled with an SA reference and target circuit, generates a sharp transition when VDD ramps up, using standard CMOS process without complex analog circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If delay type POR circuit with RC element is used, then the POR can be generated, but the area becomes large and the circuit is limited to fast ramping rates
Solution Approach 1:
The patent changes the fundamental operating parameters from RC time constant-based delay to sense amplifier gain-based sharp transition. By using high-gain sense amplifiers with controlled threshold voltages, the circuit achieves POR generation without large RC components, significantly reducing area while maintaining reliability across wide ramping rates.
Solution Approach 2:
The patent replaces the passive RC mechanical timing system with an active sense amplifier-based voltage sensing system. This substitution enables precise threshold detection and sharp transitions without the area penalties of large resistors and capacitors, resolving the contradiction between reliability and area.
2Measurement precision
If voltage reference circuit with bipolar devices and OPAMP is used, then precision POR can be achieved, but the circuit complexity increases
Solution Approach 1:
The patent replaces expensive, complex bipolar devices and operational amplifiers with simple CMOS sense amplifier circuits. The sense amplifiers achieve sufficient precision for POR generation without requiring the complex analog circuitry of traditional voltage reference circuits, significantly reducing device complexity while maintaining adequate turn-on voltage precision.
Solution Approach 2:
The patent extracts only the essential function of voltage threshold detection from complex voltage reference circuits. By using sense amplifiers that simply compare voltages and amplify the difference, the design achieves precision POR without the unnecessary complexity of bipolar devices and full operational amplifiers.
3Reliability
If POR circuit follows VDD ramping closely, then the POR can be generated, but the transition becomes slow and unsharp
Solution Approach 1:
The patent employs positive feedback through high-gain sense amplifiers. When the VDD reaches the threshold voltage, the sense amplifier detects the small voltage difference and amplifies it rapidly, creating a sharp regenerative transition. This feedback mechanism ensures reliable POR generation while achieving very fast transition speeds, resolving the contradiction between reliability and speed.
Solution Approach 2:
The patent exploits the regenerative oscillation inherent in high-gain differential amplifiers. The sense amplifier circuit naturally oscillates between saturation states when triggered, producing a sharp, rapid transition from low to high voltage. This inherent oscillation mechanism provides both reliable POR generation and extremely fast transition speeds.
Data Source
AI summary
A Power-On Reset (POR) design that provides a sharply rising signal when a supply voltage VDD ramps up from 0V to a pre-determined value for system reset. The POR design has at least one of sense amplifier (SA) bias circuit, a SA reference circuit, a SA target circuit, and a SA. When VDD ramps up, the SA bias circuit, the SA reference circuit, the SA target circuit, and the SA are turned on. The SA is configured to receive a SA reference input and a SA target input and to compare the SA reference input with the SA target input to generate a SA output. The SA output can rise sharply when VDD reaches a predetermined value. The SA output can be buffered to generate a POR signal.