Current Mirror Voltage Clamp for High Load Impedance Saturation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current mirrors, particularly the Wilson current mirror, experience a drop in performance when faced with high load impedances due to transistor saturation, which is exacerbated by the inherent characteristics of transistors used in these circuits.
Innovation Solution
Incorporating a second set of transistors acting as a voltage clamp or voltage comparator, which drives current from a power source to prevent saturation in the primary current mirror transistors, ensuring they remain in the active region and avoid saturation, even at high load impedances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a Wilson current mirror configuration is used to achieve high performance current mirroring, then current matching precision is improved, but transistor saturation occurs at high load impedances causing performance degradation
Solution Approach 1:
The current mirror circuit is divided into two functional segments: a first set of transistors (Q1, Q2) forming the core current mirror, and a second set of transistors (Q3, Q4) forming a voltage clamp circuit. This segmentation allows each segment to perform its specialized function independently, preventing saturation in the core mirror transistors while maintaining current matching precision.
Solution Approach 2:
The second set of transistors (Q3, Q4) acts as an intermediary voltage clamp circuit that mediates between the power source and the core current mirror. This intermediary prevents excessive voltage buildup that would cause saturation in the core transistors, thereby maintaining reliable operation at high load impedances without compromising current matching.
2Device complexity
If standard current mirror transistors are used to maintain simplicity, then device complexity is reduced, but saturation occurs at high load impedances limiting applicability
Solution Approach 1:
The second set of transistors (Q3, Q4) serves multiple functions simultaneously: it acts as a voltage clamp to prevent saturation, provides an additional current path for high impedance loads, and maintains the operational integrity of the core current mirror. This multi-functionality enhances adaptability across different impedance ranges without significantly increasing overall circuit complexity.
3Reliability
If voltage clamp transistors are added to prevent saturation, then reliability at high load impedance is improved, but device complexity increases
Solution Approach 1:
The voltage clamp function is merged with the current mirror functionality by using the second set of transistors (Q3, Q4) that are coupled to the same power source and share common circuit nodes with the core mirror transistors. This merging approach achieves saturation prevention while minimizing the increase in overall device complexity through shared circuit resources.
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 maintains the dynamic response and prevents performance drops at high load impedances, allowing current mirrors to function effectively across a wide range of impedances without saturation, enhancing their applicability in high-speed and high-dynamic-range applications.
Implementation Method 1
ensuring they remain in the active region and avoid saturation, even at high load impedances
Data Source
AI summary
A current mirror comprises first and second sets of transistors. each of the first and second sets is a matched set comprising a first transistor and a second transistor. For each set, the base of the first transistor is directly coupled to the base of the second transistor. For one of the first and second transistors of each set the base is directly coupled to the collector. The collectors of the first and second transistors of the first set are coupled, respectively, to the emitters of the first and second transistors of the second set in series. A current output of the current mirror is coupled between the collector of the second transistor of the first set and the emitter of the second transistor of the second set.