MOS Input Threshold Circuit for Above-Supply Voltage Detection
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Solution Overview
Problem
Conventional input devices struggle to accurately determine whether a voltage value of an input signal is higher or lower than a threshold value when the threshold value exceeds the power supply voltage, due to limitations in resistance dividing circuits and comparator circuits.
Innovation Solution
An input device comprising MOS transistors, resistors, and a comparator circuit, driven by reference voltages, which outputs a signal level corresponding to the state of the input signal relative to the threshold value, with specific resistor and current source configurations to enhance accuracy and input impedance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a resistance dividing circuit is used to generate a voltage value proportional to the input signal voltage, then the circuit can compare the voltage with a threshold value, but it cannot accurately determine whether the voltage value is higher or lower than the threshold value when the threshold value is higher than the power supply voltage
Solution Approach 1:
The patent introduces a second MOS transistor as an intermediary element that mirrors the first MOS transistor's characteristics. This second transistor, with its gate connected to the first reference terminal and drain to the signal input terminal, creates a reference current path that enables accurate voltage comparison even when the threshold exceeds the power supply voltage. The intermediary transistor translates the high threshold voltage comparison into a measurable current signal.
Solution Approach 2:
The patent changes the operating parameters by using current-mode signaling instead of direct voltage comparison. By converting the voltage comparison problem into a current comparison problem through the MOS transistor pair and resistors, the system can accurately determine voltage relationships even when voltages exceed the power supply range. The resistor values are specifically chosen to transform voltage differences into proportional current signals.
2Ease of operation
If conventional comparator circuits are used, then the device can output a signal level corresponding to voltage comparison, but it cannot accurately determine the voltage state when the threshold value exceeds the power supply voltage
Solution Approach 1:
The patent moves the comparison operation from the voltage domain to the current domain, adding a dimensional transformation to the measurement process. By using MOS transistors to convert voltage signals into current signals, the system can perform accurate comparisons in the current domain even when the original voltage thresholds exceed the power supply voltage. This dimensional change allows the comparator to operate accurately in regimes where direct voltage comparison would fail.
3Adaptability or versatility
If the threshold value is set higher than the power supply voltage, then the input device can detect higher voltage states, but conventional circuits cannot accurately determine whether the input signal voltage is higher or lower than the threshold value
Solution Approach 1:
The patent replaces direct voltage measurement mechanics with current-based measurement mechanics. Instead of directly comparing voltages that exceed the power supply voltage, the system uses MOS transistors to convert the voltage comparison task into a current comparison task. This substitution allows reliable operation with high threshold voltages by operating in a regime (current mode) that is not constrained by the power supply voltage limit.
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
Enables accurate determination of the input signal's state relative to the threshold value, even when the threshold is higher than the power supply voltage, by optimizing resistor and current source values to reduce variations and improve input impedance.
Implementation Method 1
The comparator circuit has a first input terminal, a second input terminal, and an output terminal which is the signal output terminal of the input device. The first input terminal is electrically connected to the first node and set at the same voltage as the first node. The second input terminal is electrically connected to the second node and set at the same voltage as the second node. The output terminal outputs a signal having a level corresponding to a state in which a voltage of the second input terminal is higher than a voltage of the first input terminal or a level corresponding to a state in which the voltage of the second input terminal is lower than the voltage of the first input terminal.
Data Source
AI summary
The embodiment relates to an input device comprises first and second MOS transistors, first to fourth resistors, and a comparator circuit. The first MOS transistor has a drain connected to a first terminal having a first voltage, a gate connected to a signal input terminal, and a source connected to a second terminal having a second voltage via the first and third resistors. The second MOS transistor has a drain and a gate connected to the first terminal, and a source connected to the second terminal via the second and fourth resistors. The comparator circuit outputs a signal having a level corresponding to a state in which a voltage of a node between the first and third resistors is higher or lower than a voltage of a node between the second and fourth resistors.