PTAT Power-On-Reset Circuit for Fast Low-Power Threshold Detection
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Solution Overview
Problem
Existing power-on-reset (POR) circuits face challenges in generating reference voltages higher than the bandgap voltage, experiencing significant static consumption, and having long time delays for power supply detection, which are inadequate for applications requiring low dispersion, low static consumption, noise immunity, and fast reset signal generation.
Innovation Solution
A POR circuit based on a PTAT stage with a PTAT generator, output comparator, and Schmitt trigger, utilizing a central branch with variable resistance values to achieve POR detection levels higher than the bandgap voltage, minimizing static power consumption, and ensuring rapid response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If dedicated band-gap voltage generators are used to generate reference voltages, then the POR detection levels can be generated, but the static power consumption increases significantly
Solution Approach 1:
The patent extracts the band-gap voltage generation function from a dedicated band-gap voltage generator and implements it using a simplified circuit comprising a PTAT generator and a comparator. This extraction eliminates the need for complex band-gap circuitry while maintaining the ability to generate accurate POR detection levels, thereby significantly reducing static power consumption.
Solution Approach 2:
The patent changes the approach from using a fixed band-gap voltage reference to using a PTAT (Proportional To Absolute Temperature) voltage that varies with temperature. By using the relationship between PTAT voltage and temperature along with a comparator threshold, the circuit achieves POR detection functionality with much lower power consumption than traditional band-gap generators.
2Reliability
If traditional POR circuits are used, then POR detection is achieved, but the time delay for detection is too long for fast power supply ramps
Solution Approach 1:
The patent replaces the mechanical-like charging/discharging process of traditional POR circuits with an electronic comparison process. The comparator directly compares the PTAT voltage with a reference threshold voltage, providing nearly instantaneous detection without the time delays associated with capacitor charging or complex logic circuit propagation delays.
3Measurement precision
If band-gap voltage generators are used, then reference voltages can be generated, but it is difficult to generate reference voltages higher than the band-gap voltage
Solution Approach 1:
The patent uses a dynamic PTAT voltage that increases with temperature rather than a fixed band-gap voltage. This dynamic characteristic allows the circuit to achieve detection levels above the traditional band-gap voltage by utilizing the temperature-dependent nature of the PTAT generator in conjunction with the comparator's threshold setting.
4Adaptability or versatility
If POR circuits operate in extended power supply ranges, then adaptability is improved, but noise immunity deteriorates due to power supply fast variations
Solution Approach 1:
The patent implements hysteresis through the comparator's feedback mechanism, where the threshold voltage is set such that the comparator switches states at different voltage levels for rising versus falling power supply conditions. This feedback-based hysteresis creates a noise margin that prevents spurious triggering from fast power supply variations while maintaining operation across extended power supply ranges.
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 improved POR detection levels with low dispersion and fast response, achieving low static consumption, high noise immunity, and precise control over POR detection thresholds, suitable for extended power supply ranges and varying temperatures.
Implementation Method 1
A POR circuit based on a PTAT stage with a PTAT generator, output comparator, and Schmitt trigger
Data Source
AI summary
An embodiment power-on-reset circuit, having a power supply input to receive a power supply voltage, generates a reset signal with a value switching upon the power supply voltage crossing a POR detection level. The power-on-reset circuit has: a PTAT stage having a left branch and a right branch and generating a current equilibrium condition between the currents circulating in the left and right branches upon the power supply voltage reaching the POR detection level; and an output stage coupled to the PTAT stage and generating the reset signal, with the value switching at the occurrence of the current equilibrium condition for the PTAT stage. The power-on-reset circuit further comprises a detection-level generation stage, coupled to the PTAT stage as a central branch thereof to define the value of the POR detection level.