Class-AB Amplifier Circuit With Integrated Minimum Selector
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Solution Overview
Problem
Existing amplifier circuits with class-AB output stages require additional stages for current control, leading to increased complexity and chip area, while aiming for low distortion and high gain, which complicates their implementation in compact designs.
Innovation Solution
The amplifier circuit integrates a differential input stage with cross-coupled current mirrors and a minimum selector circuit, eliminating the need for an extra intermediate stage to achieve class-AB behavior, thus reducing circuit area and supply current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an extra intermediate stage is added to control minimum current in output stage transistors, then class-AB behavior and distortion performance are improved, but circuit area and device complexity increase
Solution Approach 1:
The patent combines the minimum selector circuit directly with the current mirror circuit, eliminating the need for a separate intermediate control stage. The minimum selector shares circuit elements with the current mirror, integrating multiple functions into a unified structure that maintains class-AB behavior while reducing overall circuit complexity and area.
Solution Approach 2:
The current mirror circuit is designed to serve multiple functions simultaneously: it provides current amplification, implements class-AB biasing through the integrated minimum selector, and controls the minimum current in output stage transistors. This multi-functionality eliminates the need for dedicated separate stages for each function.
2Reliability
If feedback circuits with minimum selectors are used to control quiescent current accurately, then distortion performance improves, but device complexity increases due to extra transistors needed for current comparison and conversion
Solution Approach 1:
The minimum selector circuit is merged with the current mirror circuit, sharing transistors and circuit elements between the two functions. This integration dramatically reduces the total number of transistors required compared to implementing these as separate stages, while maintaining accurate quiescent current control.
3Device complexity
If a compact two-stage amplifier is designed with common source output transistors and class-AB behavior, then circuit area is reduced, but achieving accurate class-AB current control becomes more difficult
Solution Approach 1:
The patent achieves accurate class-AB current control in a compact two-stage amplifier by merging the minimum selector with the current mirror in the second stage. This integration provides the necessary current control functionality without adding extra stages, making accurate class-AB implementation feasible in compact designs.
Data Source
Figure 1~2
Figure 3
AI summary
An amplifier circuit, comprising a differential input stage (M1, M2), two cross-coupled current mirrors (M3,M4; M5,M6) coupled to respective outputs of the differential input stage (M1, M2), and a minimum selector circuit (M11, M12, M13, M14) coupled to outputs of the current mirrors.