Amplifier Output Stage DC Shifting for Low Quiescent Current
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Solution Overview
Problem
Conventional linear amplifiers face a trade-off between quiescent current and linearity due to direct coupling of the amplifier and power stages, leading to compromised signal swings and linearity when transistors are designed for low quiescent current.
Innovation Solution
Incorporating a DC-shifting stage and compensation network to de-couple the amplifier and power stages, using feedforward paths to adjust DC voltages and preserve AC signals, thereby maintaining linearity while reducing quiescent current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the transistors of the power stage are designed to have small gate-source voltages to lower the quiescent current, then the quiescent current is reduced, but the linearity of the amplifier stage deteriorates and the swings of output signals become smaller
Solution Approach 1:
The invention divides the direct coupling between amplifier stage and power stage into separate segments by introducing a DC-shifting stage. This segmentation allows independent optimization of each stage: the amplifier stage can maintain large signal swings for good linearity, while the power stage can operate with small gate-source voltages for low quiescent current. The DC-shifting stage acts as an intermediary that decouples the DC operating points of the two stages.
Solution Approach 2:
The DC-shifting stage serves as an intermediary component between the amplifier stage and power stage. It receives signals from the amplifier stage, adjusts their DC voltage levels through its circuitry (including resistors and capacitors), and provides the adjusted signals to the power stage. This intermediary function enables the amplifier stage to operate with optimal DC conditions for linearity while the power stage receives signals with DC levels optimized for low quiescent current operation.
2Use of energy by moving object
If the transistors of the power stage are designed to have small gate-source voltages to lower the quiescent current, then the quiescent current is reduced, but the swings of output signals become smaller
Solution Approach 1:
By segmenting the signal path with a DC-shifting stage, the invention allows the amplifier stage to generate large signal swings independently of the power stage's quiescent current requirements. The DC-shifting stage preserves these large swings while adjusting only the DC voltage levels, enabling the power stage to operate with small gate-source voltages without compromising signal swing amplitude.
Solution Approach 2:
The DC-shifting stage acts as an intermediary that selectively modifies only the DC voltage components of the signals while leaving the AC signal swings intact. This allows the amplifier stage to produce large signal swings for high productivity, while the power stage receives DC-adjusted signals that enable low quiescent current operation without reducing the actual signal swing magnitude.
Data Source
AI summary
The present invention provides a linear amplifier including an amplifier stage, a DC-shifting stage, a compensation network and a power stage. The amplifier stage is configured to generate a first signal and a second signal. The DC-shifting stage is configured to adjust a DC voltage of the first signal and a DC voltage of the second signal to generate an adjusted first signal and an adjusted second signal. The compensation network is configured to generate a first driving signal and a second driving signal according to the first signal, the second signal, the adjusted first signal and the adjusted second signal. The power stage is configured to generate an output signal according to the first driving signal and the second driving signal.