Input Circuit Hysteresis Using Current-Driven Threshold Switching
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional input circuits exhibit hysteresis that is dependent on power-supply voltage, leading to inconsistent signal transitions.
Innovation Solution
An input circuit design featuring a PMOS transistor, an NMOS transistor, a current source, a current mirror, and a switch, where the threshold voltage is determined by the current drivability of the NMOS transistor and the current source, allowing for hysteresis without power-supply voltage dependence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the conventional input circuit uses PMOS transistors with power-supply voltage applied between gate and source, then the hysteresis function is achieved, but power-supply voltage dependence is introduced
Solution Approach 1:
A current source is introduced as an intermediary element to provide a reference current that is independent of power-supply voltage variations. This current source mediates between the power supply and the differential pair, ensuring that the hysteresis threshold remains stable regardless of power-supply fluctuations. The current source acts as a buffer that isolates the hysteresis function from power-supply voltage dependence.
Solution Approach 2:
The invention changes the controlling parameter from voltage-driven (conventional PMOS operation with VDD-VSS applied to gate-source) to current-driven (using a current source to set the operating point). By changing from voltage control to current control, the hysteresis threshold becomes determined by current ratios rather than voltage levels, thereby eliminating power-supply voltage dependence while maintaining the hysteresis function.
2Reliability
If the threshold voltage is determined by current drivability of input transistors, then hysteresis without power-supply voltage dependence is achieved, but device complexity increases
Solution Approach 1:
The current source serves multiple functions simultaneously: it sets the operating current for the differential pair, establishes the hysteresis threshold through current mirroring, and provides power-supply voltage isolation. By making this single element multi-functional, the patent avoids adding excessive complexity while achieving power-supply independence. The current mirror also serves dual purposes of current replication and threshold determination.
Data Source
AI summary
An input circuit includes a first input transistor and a second input transistor connected to an input terminal; a current source which makes a current flow in the second input transistor through a current mirror; a switch provided between the current mirror and the current source, and having a switch control terminal connected to the drain of the first input transistor; and a transistor connected to the first input transistor, on/off of the transistor being controlled by an output signal, wherein a current drivability of the second input transistor is switched by an output signal, and a threshold voltage to the input signal is determined based on the current drivability of the second input transistor and the current source.