Power-On Reset Circuit With Precise Thresholds and Low Static Current
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Solution Overview
Problem
Existing power-on reset (POR) circuits either consume constant current, leading to high power losses (level-based PORs), or require a minimum power supply dV/dt and have ill-defined detection levels (delay-based PORs).
Innovation Solution
A POR circuit utilizing a combination of transistors configured into a feedback loop and a comparator with a voltage supply-dependent threshold, generating a POR pulse during power supply ramp-up between adjustable voltage levels, independent of power supply dV/dt, and consuming minimal or no static current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If level-based POR circuits are used, then detection accuracy is improved, but power consumption increases due to constant current
Solution Approach 1:
The POR circuit uses periodic action by implementing delay-based detection mechanisms that activate only during power-up transitions. The circuit employs multiple delay paths (first delay path with first resistor-capacitor pair, second delay path with second resistor-capacitor pair) that create time-dependent detection windows, allowing the circuit to detect voltage levels only during the power-on transition period rather than continuously, thus reducing power consumption while maintaining detection accuracy.
2Use of energy by moving object
If delay-based POR circuits are used, then power consumption is reduced, but detection precision deteriorates due to ill-defined detection levels
Solution Approach 1:
The POR circuit uses intermediary elements (resistor-capacitor pairs acting as delay elements) to mediate between the power supply voltage and the detection logic. These intermediaries create controlled time delays that define precise detection moments, transforming the ill-defined delay-based detection into well-defined detection levels. The first and second resistor-capacitor pairs serve as intermediaries that shape the voltage transitions and provide clear detection thresholds.
Solution Approach 2:
The detection function is segmented into multiple independent delay paths with different detection thresholds. The first delay path detects one voltage level while the second delay path detects another voltage level, allowing the circuit to provide multiple well-defined detection levels. This segmentation enables precise detection at different voltage thresholds without requiring continuous high-power operation.
3Reliability
If constant current is used in POR circuits, then detection reliability is improved, but power loss increases
Solution Approach 1:
The circuit employs periodic action by using delay-based detection that activates only during power-up transitions rather than maintaining constant current flow. The resistor-capacitor pairs create time-dependent detection windows, allowing reliable detection to occur periodically during transitions while minimizing continuous power consumption, thus reducing power loss while maintaining detection reliability.
4Measurement precision
If multiple delay paths are added to improve detection precision, then detection accuracy is improved, but device complexity increases
Solution Approach 1:
The circuit merges multiple functions into unified delay path structures. Each delay path combines resistance and capacitance elements that simultaneously provide both the delay function and the voltage division function. The first resistor-capacitor pair and second resistor-capacitor pair are integrated into the overall POR circuit architecture, where they serve dual purposes of creating detection delays and establishing voltage thresholds, thereby improving detection accuracy without proportionally increasing complexity.
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 provides well-defined detection levels and minimal power consumption, generating a POR pulse only during power supply ramp-up, thus reducing power losses and improving detection accuracy.
Implementation Method 1
a capacitor having a first end coupled to a second circuit and a second end coupled to the resistor divider
Implementation Method 2
a comparator coupled to the power supply input and the reference potential, and having a comparator threshold dependent upon the power supply voltage
Data Source
Figure 1
Figure 2A
Figure 2B
AI summary
One example discloses a power on reset (POR) circuit, wherein a first circuit is configured to un-couple a power supply input from a resistor divider when the voltage on a second end of the capacitor is above a first circuit threshold; a second circuit configured to couple the second end of the capacitor to the power supply input when a voltage on at least one tap point of the resistor divider is above a second circuit threshold; wherein the comparator is coupled to at least one of the tap points, the reference potential, and a POR output; and wherein the comparator is configured to ramp-up a FOR signal on the POR output when a voltage on the at least one of the tap points is greater than the comparator threshold.