Hysteresis Input Circuit With Supply-Independent Threshold Control
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Solution Overview
Problem
Existing input circuits with hysteresis characteristics exhibit power supply voltage dependency in their thresholds, which becomes a problem when operating with low voltage microcomputers, causing incorrect signal recognition.
Innovation Solution
An input circuit design featuring an input transistor and a current source connected in series, where the current value of the current source is adjusted based on the output signal to determine the threshold, independent of the power supply voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the transistor 503 is ON-controlled by the magnitude of VDD to obtain hysteresis characteristics, then the threshold at L-to-H transition is higher than at H-to-L transition, but the threshold exhibits power supply voltage dependency causing incorrect recognition with low voltage microcomputers
Solution Approach 1:
The patent changes the control parameter from voltage-based (VDD magnitude) to current-based (current source magnitude). By controlling the current source 102 with the output signal instead of controlling transistor 503 with VDD, the threshold becomes independent of power supply voltage while maintaining hysteresis characteristics. This parameter substitution resolves the contradiction between reliability and adaptability.
2Reliability
If the power supply voltage of the input circuit is high to ensure proper operation, then hysteresis characteristics are maintained, but low voltage microcomputers cannot properly supply input signals
Solution Approach 1:
The invention changes the operating parameter from voltage to current. The current source 102 is controlled by the output signal to provide a current value that determines the threshold, rather than relying on high VDD. This allows the circuit to operate at low voltages while maintaining proper hysteresis functionality, resolving the contradiction between reliability and energy consumption.
3Reliability
If multiple transistors (501, 502, 503) and an inverter (504) are used to create hysteresis, then the threshold difference between transitions is achieved, but the device complexity increases
Solution Approach 1:
The patent extracts and eliminates unnecessary components from the traditional hysteresis circuit. By removing the inverter and reducing the transistor network, and instead using a simple current source 102 controlled by the output signal, the circuit achieves threshold stability with fewer components. This extraction principle resolves the contradiction between reliability and device complexity.
Data Source
AI summary
To provide an input circuit which avoids power supply voltage dependency of a threshold of the input circuit when an output signal is transited. There is provided an input circuit equipped with an input transistor and a current source connected in series between a first power supply and a second power supply. The input circuit is configured in such a manner that an input signal is inputted to a gate of the input transistor and a signal of a connection point between the input transistor and the current source is outputted as an output signal, and a current value of the current source is changed based on the output signal.