Single-Stage Amplifier With Dual Common-Mode Control Loops
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Solution Overview
Problem
Existing amplifier designs face challenges in achieving a wide input common-mode range while maintaining low noise and high gain, particularly when coupled with magnetic sensors, due to issues like resistance drift over temperature and process variations, which affect the common-mode voltage range and sensor gain.
Innovation Solution
The described amplifier architecture incorporates a voltage output common-mode control circuit and a voltage input common-mode control circuit, which operate continuously and provide isolation between input terminals and control circuits, allowing for continuous time-varying control signals and operating at different frequencies to stabilize the system, thereby enhancing the input common-mode voltage range and reducing noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional amplifier designs are used, then the circuit is simple, but the input common-mode voltage range is limited and noise performance deteriorates
Solution Approach 1:
The amplifier is divided into multiple functional stages: a first amplification stage with differential input transistors, a second amplification stage with differential output transistors, and separate common-mode control circuits. This segmentation allows each stage to be optimized independently, expanding the input common-mode voltage range without proportionally increasing overall complexity.
Solution Approach 2:
Common-mode control circuits are introduced as intermediary elements between the input/output terminals and the amplification stages. These control circuits generate common-mode control signals that regulate the operating points of the differential pairs, enabling wider input common-mode voltage range while maintaining stable amplification performance.
2Reliability
If conventional amplifier designs are used, then production costs are low, but noise performance and gain are insufficient
Solution Approach 1:
Common-mode feedback loops are implemented where the common-mode control circuits continuously monitor the differential input and output terminals, compare them against reference voltages, and adjust the common-mode control signals accordingly. This feedback mechanism stabilizes the noise performance and maintains consistent gain across varying input common-mode voltages.
Solution Approach 2:
The amplifier utilizes parameter changes in the common-mode control signals to optimize performance. By dynamically adjusting the common-mode voltage levels at different operating conditions, the amplifier maintains low noise and high gain across a wide input common-mode voltage range while using standard manufacturing processes.
3Measurement precision
If resistance drift compensation is added, then measurement precision improves, but device complexity increases
Solution Approach 1:
The common-mode control circuits automatically compensate for resistance drift effects by continuously regulating the common-mode voltages. The circuits self-adjust the operating points of the differential pairs based on real-time conditions, maintaining stable sensor gain without requiring external compensation mechanisms or additional complex circuitry.
Data Source
AI summary
In some examples, an amplifier includes a pair of input differential transistors a pair of feedback transistors, a pair of current sources, a pair of gain setting resistors, and a tail current transistor. Control terminals of the feedback transistors are respectively coupled to first terminals of the input differential transistors. The pair of current sources are respectively coupled to the control terminals of the feedback transistors and the first terminals of the input differential transistors. The pair of gain setting resistors have first terminals that are respectively coupled to the second terminals of the input differential transistors. The pair of gain setting resistors have second terminals that are coupled to one another. The tail current transistor has a first terminal coupled to the second terminals of the gain setting resistors and a second terminal coupled to a DC supply.