Current Mirror Feedback Circuit for High Output Impedance
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Solution Overview
Problem
Current mirror circuits in low-voltage power supply applications face challenges in maintaining output impedance due to limited headroom, making it impractical to use cascode output stages.
Innovation Solution
The implementation of a feedback circuit that adjusts the voltage level of the control node in a current mirror circuit based on the output node voltage, thereby modifying the mirror current to maintain its desired level despite changes in output voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a cascode output stage is used to increase output impedance, then output impedance is improved, but voltage headroom requirement increases making it impractical for low-voltage applications
Solution Approach 1:
The patent implements a feedback circuit that senses the output voltage and adjusts the control node voltage accordingly. The feedback circuit includes a transistor whose gate is connected to the output node, creating a feedback loop that automatically compensates for output voltage changes. This feedback mechanism increases output impedance without requiring additional voltage headroom, as it uses the existing output voltage signal to control the mirror current stabilization.
2Stability of the object's composition
If the control node voltage is fixed to maintain mirror current, then current stability is improved, but output impedance decreases causing current variation with output voltage changes
Solution Approach 1:
The feedback circuit dynamically adjusts the control node voltage based on output voltage changes. When output voltage increases, the feedback transistor conducts more current, which adjusts the control node voltage to maintain constant mirror current. This dynamic adjustment maintains both current stability and high output impedance, as the control voltage is continuously optimized rather than fixed.
Solution Approach 2:
The feedback transistor acts as an intermediary element between the output node and the control node. It transfers information about output voltage changes to the control node, enabling indirect control of the mirror current. This intermediary mechanism allows the circuit to maintain current stability while presenting high impedance to the output, as the control voltage is modulated through the feedback path rather than being directly coupled.
Data Source
AI summary
A current mirror circuit included in a computer system that includes a mirror stage circuit and a feedback circuit is disclosed. The mirror stage circuit generates a mirror current in an output node using a reference current. The feedback circuit adjusts the value of the mirror current based on a voltage level of the output node to increase the output impedance of the current mirror circuit.