Differential Amplifier Common-Mode Circuit Using a Reversible Current Mirror
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Solution Overview
Problem
In analog-to-digital conversion circuits, particularly in battery-powered systems, the challenge lies in reducing power consumption while maintaining low noise and stability, especially in the voltage reference circuitry where common-mode feedback is problematic due to low quiescent current requirements, leading to instability and increased thermal noise.
Innovation Solution
The implementation of a reversible current mirror circuit within the common-mode circuitry, which sets the common-mode voltage and operates efficiently with low quiescent current, reducing noise and increasing the quiescent current available to the reference voltage circuit, thereby stabilizing the amplifier and reducing thermal noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If common-mode feedback is used in voltage reference circuitry, then common mode voltage control is improved, but stability deteriorates due to low quiescent current requirements
Solution Approach 1:
The patent extracts the common-mode control function from the main amplifier circuit by implementing a separate common-mode feedback path. This dedicated feedback path allows independent optimization of common-mode voltage control without compromising the stability of the main voltage reference circuit, resolving the contradiction between precise common-mode control and circuit stability.
Solution Approach 2:
The patent introduces an intermediary common-mode feedback circuit that acts as a mediator between the differential output stage and the voltage reference circuitry. This intermediary structure provides the necessary common-mode control while isolating the main circuit from destabilizing feedback effects, enabling both precise control and stability to coexist.
2Use of energy by moving object
If quiescent current is reduced in voltage reference circuitry, then power consumption is improved, but thermal noise increases
Solution Approach 1:
The patent segments the circuit into distinct functional blocks with separate current domains. The voltage reference circuitry operates in a low-current mode for minimal power consumption, while dedicated noise-reduction circuitry and buffering stages provide the necessary current drive without adding to the reference circuit's power consumption. This segmentation allows the system to achieve low power consumption while maintaining low thermal noise through architectural separation rather than current increase.
Data Source
AI summary
An amplifier includes a first stage and a second stage. The first stage includes a first output, and a second output. The second stage includes a first transistor, a second transistor, and a common-mode circuit. The first transistor includes a drain coupled to the first output of the first stage. The second transistor includes a drain coupled to the second output of the first stage. The common-mode circuit includes a reversible current mirror circuit coupled to the drain of the first transistor and the drain of the second transistor.