Current Mirror Circuit Body Voltage Feedback for Line Regulation
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Solution Overview
Problem
Current mirror circuits face a tradeoff between minimizing dropout voltage and supply sensitivity, with shorter gate lengths improving dropout voltage but compromising line regulation, and existing configurations either increase die size or are impractical for low supply voltages.
Innovation Solution
A current mirror circuit that adjusts the body-to-source voltage of an input device in response to the drain-to-source voltage of an output device using a feedback circuit component, comprising transistors and resistors, to maintain constant output current despite changes in supply voltage, thereby reducing dropout voltage and improving line regulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gate length of the output transistor is minimized to reduce dropout voltage, then dropout voltage is reduced, but supply sensitivity increases and line regulation deteriorates
Solution Approach 1:
The patent implements a feedback mechanism where the body voltage of the output transistor is dynamically adjusted based on the drain voltage. Specifically, the body voltage is set to track a fraction of the drain voltage, creating a feedback loop that compensates for supply voltage variations. This feedback approach allows the use of minimum gate length transistors while maintaining good line regulation, as the feedback actively corrects for the increased supply sensitivity that would otherwise result from short channel effects.
2Ease of operation
If DC gain of the amplifier is increased to reduce supply sensitivity, then supply sensitivity is reduced, but feedback stability requires gain to roll-off at higher frequencies, increasing supply sensitivity with frequency
Solution Approach 1:
The patent changes the operating parameters of the output transistor by dynamically adjusting its body voltage rather than relying solely on increasing amplifier DC gain. By modulating the body voltage to track the drain voltage, the effective threshold voltage and channel characteristics are changed, providing supply sensitivity compensation across a wide frequency range without requiring high DC gain that would conflict with feedback stability requirements.
3Reliability
If conventional current mirror configurations are used to maintain constant output current, then output current stability is achieved, but die size increases or the circuit becomes impractical for low supply voltages
Solution Approach 1:
The patent implements a self-service mechanism where the output transistor's body voltage automatically tracks its own drain voltage through the feedback arrangement. This self-regulating behavior eliminates the need for external biasing circuits or additional transistors that would be required in conventional current mirror configurations, achieving output current stability with minimal die area and compatibility with low supply voltages.
Data Source
AI summary
A current mirror circuit that is configured to adjust a body to source voltage of an input device in response to a drain to source voltage of an output device is disclosed. In an implementation, the current mirror circuit comprises a current mirror including an input device and an output device coupled together. The current mirror circuit also includes a feedback circuit component coupled between the output of the current mirror and the input device. The feedback circuit component is configured to adjust a body to source voltage of the input device in response to a drain to source voltage of the output device.