Bandgap POR Circuit Compensation for Parasitic Substrate Currents
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Solution Overview
Problem
Conventional power on reset (POR) circuits are susceptible to external interferences such as high temperature, electromagnetic interference (EMI), and stray light, leading to parasitic substrate currents that can cause unintended reset failures, especially in industrial, automotive, and optoelectronic applications.
Innovation Solution
A POR circuit design that incorporates first and second compensation transistors to counteract parasitic currents, ensuring symmetric pull-up and pull-down current contributions at the output terminal, thereby stabilizing the tripping point and preventing false resets. This is achieved through a bandgap circuit with current mirrors and a resistive network that compensates for leakage, photoelectric, and lateral substrate currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional POR circuit is used, then the circuit can detect power supply voltage level, but the circuit is susceptible to external interferences causing parasitic substrate currents and false resets
Solution Approach 1:
The patent converts the harmful parasitic substrate currents into a beneficial compensation mechanism. By introducing compensation transistors that generate compensating currents equal in magnitude but opposite in direction to the parasitic currents, the harmful effect is transformed into a corrective action that stabilizes the POR circuit output against external interferences
Solution Approach 2:
The compensation transistors are configured to preemptively counteract the parasitic substrate currents before they can cause false resets. The compensating currents are generated in advance to balance the parasitic effects, preventing the output from reaching the tripping point due to external interferences
2Measurement precision
If bandgap circuit with current mirrors is used, then the tripping point can be determined based on bandgap voltage, but external interferences cause unsymmetric parasitic contributions to pull-up and pull-down currents
Solution Approach 1:
The patent intentionally introduces asymmetric compensation elements to counterbalance the asymmetric parasitic effects. The compensation transistors are configured with specific collector areas and current mirror ratios that create a controlled asymmetry to offset the unsymmetric parasitic contributions from external interferences, restoring overall current balance at the output terminal
3Measurement precision
If POR circuit is made more sensitive to detect voltage changes, then the reset detection capability is improved, but the circuit becomes more susceptible to false triggers from external interferences
Solution Approach 1:
The compensation transistors form a feedback mechanism that continuously monitors and counteracts parasitic current effects. The compensating currents are automatically adjusted to balance the parasitic contributions, providing negative feedback that stabilizes the output against false triggers while preserving the circuit's sensitivity to genuine voltage changes
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 POR circuit operates more robustly and accurately, maintaining a stable tripping point even under external interferences, reducing the likelihood of false resets and ensuring reliable operation in harsh environments.
Implementation Method 1
A conventional POR circuit includes a bandgap arrangement that determines a tripping point based on the bandgap voltage of silicon which can be reliably reproduced with a corresponding arrangement of bipolar transistors
Implementation Method 2
The switching operation of a bandgap current switch in a POR circuit is based on a ratio of substantially different currents through the bipolar transistors of the bandgap circuit that form a current switch. The currents are mirrored into the output terminal to pull the output terminal to the high side or the low side voltage supply terminals
Implementation Method 3
The POR circuit may be included in an integrated circuit that is subjected to external interferences such as high temperature or electromagnetic fields when the circuit is used in an industrial or automotive environment or subjected to stray light impinging on the POR circuit when the integrated circuit is used as an optoelectronic device. Such interferences may cause parasitic substrate currents in the semiconductor substrate that incorporates the POR circuit and the integrated circuit
Data Source
AI summary
A power on reset circuit comprises terminals for reference and supply potentials and a voltage divider coupled therebetween. First and second transistors of a bandgap circuit are resistively coupled to the reference potential terminal and have bases connected to the voltage divider. Current mirrors couple the collectors of the first and second transistors to an output terminal providing an output signal indicating a power on reset condition. A first compensation transistor is coupled between the collector of one of the transistors and the reference potential terminal, and a second compensation transistor is coupled between the output terminal and the reference potential terminal to compensate the effect of parasitic substrate currents in response to an external interference.