Low-Voltage Protection Circuit With Dynamic Control Voltage Switching
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Solution Overview
Problem
Low-voltage devices in integrated circuits are vulnerable to damage from high voltage drops due to the limitations of existing cascode designs, which fail to properly manage voltage levels when the supply voltage is low, leading to potential damage of NMOS transistors.
Innovation Solution
A circuit configuration that includes a pin, a control voltage generating circuit, and a protected device, where the control voltage generating circuit generates appropriate control voltages to safely couple the pin with an internal circuit, preventing excessive voltage drops by using a first control voltage when the supply voltage is high and a second control voltage when it is low, ensuring the voltage differences remain within the device's maximum withstanding voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a cascode design with a single control voltage reference is used to protect low-voltage devices, then the device can be protected when supply voltage is high, but the device cannot be protected when supply voltage is low and external high voltage is applied
Solution Approach 1:
The patent implements dynamic control voltage selection by detecting the supply voltage level and switching between a first control voltage (when supply voltage is high) and a second control voltage (when supply voltage is low). This dynamic adaptation ensures the protected device operates within safe voltage limits under varying supply conditions, resolving the contradiction between protection capability and voltage level adaptability.
Solution Approach 2:
The patent changes the control voltage parameter based on supply voltage conditions. A voltage detection circuit monitors the supply voltage and adjusts the control voltage applied to the protected device accordingly - using a higher first control voltage when supply is high, and a lower second control voltage when supply is low. This parameter change strategy enables reliable protection across different voltage scenarios.
2Reliability
If the protected device is kept off when supply voltage is low to prevent damage, then the device is protected from overvoltage, but the device cannot transmit signals from external devices
Solution Approach 1:
The patent introduces a control voltage generating circuit as an intermediary that mediates between the supply voltage conditions and the protected device operation. This circuit generates appropriate control voltages based on supply voltage detection, enabling the protected device to operate safely in signal transmission mode when supply is high, and in protection mode when supply is low, thus resolving the contradiction between device safety and signal transmission capability.
Solution Approach 2:
The patent implements a feedback mechanism where the control voltage generating circuit continuously monitors the supply voltage level and adjusts the control voltage to the protected device accordingly. When supply voltage is detected as high, the circuit enables signal transmission; when supply voltage is low, it switches to protection mode. This feedback control resolves the contradiction by dynamically balancing safety and functionality based on real-time voltage conditions.
Data Source
AI summary
The present invention discloses a circuit capable of protecting low-voltage devices. The circuit includes: a pin configured to receive a signal of an external device; a control voltage generating circuit configured to generate a first control voltage according to a supply voltage to turn on a protected device when the supply voltage is at a high level, and generate a second control voltage according to a voltage of the pin to turn on the protected device when the supply voltage is at a low level; and the protected device configured to be turned on according to one of the first and the second control voltages and thereby electrically couple the pin with an internal circuit, in which the difference between the voltage of the pin and each of the first and the second control voltages is within a maximum withstanding voltage of the protected device.