Current Mirror Bias Trimming via Feedback Transistor Scaling
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Solution Overview
Problem
Current methods for trimming analog current references in integrated circuits are inefficient, requiring additional components and time-consuming procedures, leading to increased die area, cost, and power consumption, especially when many current references are present.
Innovation Solution
Trimming the size of the feedback circuit transistor instead of resistors to maintain a constant feedback current, which allows for proportional adjustments to other current and voltage reference transistors, reducing the need for additional trimming operations and simplifying the production process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If resistor trimming is used to trim the initial reference current, then the reference current precision is improved, but the die area, cost, and power consumption increase due to additional trimming components
Solution Approach 1:
The patent extracts the trimming function from multiple separate components and concentrates it into a single feedback circuit transistor. By trimming only this one transistor's width, the invention achieves trimming of multiple current references simultaneously, eliminating the need for multiple separate trimming components and operations.
Solution Approach 2:
The feedback circuit transistor serves multiple functions: it provides feedback for the operational amplifier and simultaneously acts as the trimming element for all current references. By adjusting its width, the invention universally trims multiple current references at once, making a single component perform multiple trimming functions.
2Measurement precision
If multiple current references are trimmed individually, then each current reference precision is improved, but the production test time increases
Solution Approach 1:
The patent merges the trimming operations for multiple current references into a single trimming action. By trimming the feedback circuit transistor, all current references are trimmed simultaneously in one operation, dramatically reducing production test time compared to individual trimming of each reference.
Solution Approach 2:
The feedback circuit transistor is designed and positioned to enable preliminary trimming that affects all current references at once. This preliminary action on a single component prepares all current references for optimal operation before final testing, reducing the need for subsequent individual adjustments.
3Measurement precision
If additional trimming components are added to trim other biases, then the bias precision is improved, but the die area increases
Solution Approach 1:
The patent extracts the bias trimming function from separate dedicated components and integrates it into the feedback circuit transistor. This single transistor performs both feedback and bias trimming functions, eliminating the need for additional trimming components and reducing die area.
Solution Approach 2:
The feedback circuit transistor is designed to universally trim multiple biases simultaneously. By adjusting its width, the invention provides precise trimming for all current references and other biases without requiring separate trimming components for each, thereby minimizing die area usage.
Data Source
AI summary
A reference current is generated by a current mirror circuit. An operational amplifier of a feedback circuit generates a control voltage for control of the feedback circuit transistor. The size of the feedback circuit transistor is trimmed, and the current through the feedback circuit transistor remains relatively constant via operation of the feedback circuit. The feedback circuit transistor is scaled in size relative to the size of current reference transistor(s) (e.g., current sources or sinks), which are tied to the same control voltage. The reference current of the current reference transistors thus varies with the size of the feedback circuit transistor. Further advantageously, transistors providing reference currents for resistor ladders can also be tied to the same control voltage, but scaled proportionally with changes in size to the feedback circuit transistor, thereby maintaining relatively constant voltage from taps of the resistor ladder, even when the feedback circuit transistor is trimmed.