Power-On Reset Circuit Using Current Comparison Across Temperature
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Solution Overview
Problem
Passive RFID tags face challenges in reliably generating a power on reset signal due to fluctuations in ambient temperature and received radio wave intensity, which can result in failure to exceed the threshold voltage for reset state cancellation.
Innovation Solution
A semiconductor device with a voltage divider circuit, transistors, and a current comparison mechanism that generates a power on reset signal by comparing currents based on divided power supply voltages, ensuring reliable reset and reset cancellation regardless of temperature fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a power on reset circuit with a fixed threshold voltage is used, then the reset function works at normal temperature, but the threshold voltage fluctuates toward high voltage side as temperature decreases, causing reset state not to be canceled when temperature is low
Solution Approach 1:
The patent changes the parameter being monitored from absolute voltage level to voltage change rate. The detection circuit monitors the rate of change of voltage (dV/dt) rather than a fixed threshold voltage, allowing the reset cancellation to occur based on the dynamic behavior of voltage rise rather than a static voltage level that would be affected by temperature variations.
Solution Approach 2:
The patent transitions from a static threshold voltage comparison to a dynamic detection mechanism that responds to the rate of voltage change. The detection circuit uses capacitive charging/discharging behavior to generate a detection signal based on how quickly the voltage rises, making the system adaptive to different operating conditions including temperature variations.
2Reliability
If the threshold voltage is set to ensure reset cancellation at low temperature, then reset works at low temperature, but the power supply voltage may not exceed the threshold when received radio wave intensity is low, preventing reset cancellation
Solution Approach 1:
The patent changes the parameter being monitored from absolute voltage level to voltage change rate. By detecting the rate at which voltage rises rather than comparing against a fixed threshold, the system can reliably detect reset cancellation conditions across different power supply voltage levels caused by varying radio wave intensities.
Solution Approach 2:
The detection circuit continuously monitors the voltage change rate and provides feedback through the detection signal to control the reset state. This feedback mechanism ensures that reset cancellation occurs dynamically when the voltage rise rate indicates sufficient power supply stabilization, adapting to different operating conditions.
3Device complexity
If a voltage divider circuit is used to generate threshold voltage, then the circuit structure is simple, but the threshold voltage has negative temperature characteristic that causes fluctuation
Solution Approach 1:
The patent extracts the temperature-sensitive threshold voltage generation function from the voltage divider circuit and replaces it with a dynamic detection mechanism. Instead of using a voltage divider that generates a fixed threshold voltage subject to temperature effects, the system uses a detection circuit that responds to the rate of voltage change, eliminating the need for a temperature-stable threshold voltage reference.
Solution Approach 2:
The patent replaces the passive voltage divider circuit (electrical component-based threshold generation) with an active detection circuit that uses capacitive charging/discharging dynamics. This substitution transforms the system from relying on electrical component characteristics (which have temperature coefficients) to relying on dynamic electrical behavior (voltage change rate) that is less sensitive to temperature variations.
Data Source
AI summary
A semiconductor device and a method of generating a power on reset signal that can reliably perform power on reset on an internal circuit and subsequently cancel the reset state regardless of environmental temperature are provided. The semiconductor device according to the disclosure includes: a voltage divider circuit dividing a power supply voltage to obtain first and second voltages having different voltage values; a first transistor receiving the first voltage at the control electrode to generate a first current; a second transistor receiving the second voltage at the control electrode to generate a second current; a current comparing part comparing the first and second currents to generate a current comparison result signal representing a comparison result; and a reset signal generating part generating a power on reset signal having a first level that prompts reset or a second level that prompts reset cancelation based on the current comparison result signal.