Operational Amplifier Common-Mode Feedback for Stable DC Levels
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Solution Overview
Problem
Existing operational amplifier circuits struggle to effectively control DC voltage levels, particularly when transistors in bias or load circuits undergo variations, as common mode feedback control is typically limited to only one of these components, leading to inadequate locking of DC voltage levels.
Innovation Solution
The operational amplifier incorporates a differential amplifier circuit with a common mode feedback circuit that generates feedback voltages to control both the bias and load circuits, ensuring effective locking of DC voltage levels by comparing common mode voltage with a reference voltage and adjusting transistor operation accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If common mode feedback control is applied to only one of the bias or load circuits, then the device complexity is reduced, but the DC voltage level control stability deteriorates when transistors experience variations
Solution Approach 1:
The patent implements common mode feedback control in both the bias circuit and load circuit. The feedback mechanism continuously monitors the common mode voltage and adjusts the bias and load circuits accordingly to maintain stable DC voltage levels even when transistor variations occur, thereby resolving the contradiction between reduced complexity and improved stability
Solution Approach 2:
The patent applies beforehand cushioning by pre-configuring dual common mode feedback control paths in both bias and load circuits. This preparatory measure ensures that when transistor variations occur, the feedback mechanisms are already in place to compensate, preventing DC voltage level instability before it can affect circuit operation
2Reliability
If dual common mode feedback control is implemented in both bias and load circuits, then the DC voltage level control stability is improved, but the device complexity increases
Solution Approach 1:
The common mode feedback control circuit is designed with multi-functionality to serve both the bias circuit and load circuit simultaneously. By making the feedback mechanism universal and applicable to both circuits, the patent achieves enhanced stability without proportionally increasing overall system complexity, as the same feedback principles and components are reused across different circuit blocks
Data Source
AI summary
An operational amplifier includes a differential amplifier circuit and a common mode feedback circuit. The differential amplifier circuit includes a bias circuit, an amplifier circuit, and a load circuit. The bias circuit generates a first operation voltage. The amplifier circuit receives a pair of input signals, and generates a pair of output signals according to the input signals and the first operation voltage. The load circuit is coupled to the amplifier circuit. The common mode feedback circuit generates at least one common mode feedback voltage based on a common mode voltage and a reference voltage. The common mode voltage is associated with the output signals. The at least one common mode feedback voltage is for controlling the bias circuit and the load circuit, to control a direct current (DC) voltage level of the differential amplifier circuit.