Hysteresis Current Source with Adjustable Resistor Differential Pair
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Solution Overview
Problem
Existing current sources with hysteresis exhibit a poor hysteresis effect and limited adaptive range, leading to instability in output circuits such as LDO regulators due to their reliance on small overdrive voltages and fixed width/length ratios in differential pairs.
Innovation Solution
A current source and supply system are designed with a tail current transistor, a resistor, and differential pairs where the bulk terminals of transistors are connected to different terminals of the resistor, allowing hysteresis control through resistance value adjustment, enhancing the hysteresis effect and adaptive range without redundant voltage sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the adaptive bias current source is excessively sensitive to the status of the output circuit, then the response speed is improved, but the output circuit becomes unstable since the current supplied always varies
Solution Approach 1:
The patent implements hysteresis feedback in the adaptive bias current source by comparing the output voltage with a reference voltage through a differential pair. The feedback mechanism creates two distinct threshold voltages (Vth1 and Vth2) for upward and downward voltage transitions, causing the bias current to remain stable within a hysteresis band rather than continuously varying. This resolves the contradiction by providing rapid response when voltage exceeds thresholds while maintaining stability during normal operation within the hysteresis range.
2Reliability
If hysteresis is achieved by applying different width/length ratios in transistors, then the hysteresis effect is obtained, but the adaptive range is limited and hysteresis effect is poor when transistors operate in sub-threshold region
Solution Approach 1:
The patent changes the controlling parameter for hysteresis from fixed transistor width/length ratios to variable voltage thresholds. By using a differential pair with adjustable reference voltage, the hysteresis bandwidth can be dynamically adjusted to match different operating conditions. This allows the system to maintain strong hysteresis effect when needed while expanding the adaptive range to accommodate various voltage levels and load conditions, resolving the contradiction between reliable hysteresis and adaptability.
3Use of energy by stationary object
If the transistors have low overdrive voltages to reduce static power consumption, then power consumption is reduced, but the hysteresis effect becomes poor
Solution Approach 1:
The patent introduces an intermediary reference voltage system that mediates between the low overdrive voltage requirement and the need for strong hysteresis effect. The differential pair compares the output voltage against adjustable reference thresholds, allowing the transistors to operate with low overdrive voltages for power efficiency while the voltage comparison mechanism provides the necessary hysteresis effect. This decouples the relationship between overdrive voltage and hysteresis strength, resolving the contradiction.
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
This configuration provides a stable current source with a wider adaptive range and improved hysteresis performance, ensuring the output circuit's stability by adjusting the resistance value to control hysteresis, reducing power consumption, and adapting to varying voltage conditions.
Implementation Method 1
a first differential pair, coupled to the first resistor, is used for controlling a magnitude of the first current supplied to the output circuit. The first differential pair comprises a first transistor, of which a bulk terminal is coupled to a terminal of the first resistor; and a second transistor, of which a bulk terminal is coupled to another terminal of the first resistor
Data Source
AI summary
A current source with hysteresis for an output circuit includes a tail current transistor, a resistor and a differential pair. The tail current transistor is used for supplying a current to the output circuit. The resistor is coupled to a drain terminal of the tail current transistor. The differential pair, coupled to the resistor, is used for controlling a magnitude of the current supplied to the output circuit. The differential pair includes a first transistor, of which a bulk terminal is coupled to a terminal of the resistor; and a second transistor, of which a bulk terminal is coupled to another terminal of the resistor.