Current Source Circuit with Feedback-Held Gates for Accurate Output
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Solution Overview
Problem
Current mirror circuits in integrated circuits suffer from deviations in output current levels due to manufacturing variations in transistor characteristics, such as threshold voltage variations, leading to inaccuracies in current control.
Innovation Solution
A current source circuit configuration that includes multiple current generation subcircuits, operational amplifiers, and storage capacitors, which maintain gate voltages of transistors to generate accurately controlled currents despite transistor characteristic variations, using resistors and operational amplifiers to regulate current levels independently of transistor threshold voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If typical current mirror circuits are used with commonly coupled gates, then the circuit structure is simple, but the output current deviates from design values due to transistor threshold voltage variations
Solution Approach 1:
The current source circuit is divided into multiple current generation subcircuits, each with its own operational amplifier and storage capacitor. This segmentation allows independent control and compensation for each transistor's threshold voltage variation, improving output current accuracy without requiring complete redesign of the entire circuit.
Solution Approach 2:
Operational amplifiers are used to detect the actual current output and provide feedback control. The operational amplifiers adjust the gate voltages of the transistors based on feedback signals, compensating for threshold voltage variations and ensuring that the output currents match the design values despite manufacturing variations.
2Manufacturing precision
If operational amplifiers and storage capacitors are added to each current generation subcircuit, then output current accuracy improves, but device complexity increases
Solution Approach 1:
The operational amplifiers and storage capacitors are designed as standardized modules that can be replicated across multiple current generation subcircuits. This universal design approach allows the same circuit topology to be used for all subcircuits, simplifying the overall design process and making the increased complexity manageable through repetition of proven functional blocks.
Data Source
AI summary
A current source circuit includes a plurality of current generation subcircuits and an operational amplifier. Each of the plurality of current generation subcircuits includes an output transistor having a drain through which an output constant current is generated, a resistor coupled between a first constant voltage node and a source of the output transistor, and a storage capacitor coupled between the first constant voltage node and a gate of the output transistor. The operational amplifier has a first input coupled to a second constant voltage node, a second input selectively couplable to the source of the output transistor, and an output selectively couplable to the gate of the output transistor.