DC-Shifting Amplifier Output Stage for Low-Current Linearity

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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 gate-source voltages.

Innovation Solution

Incorporating a DC-shifting stage and a compensation network to adjust DC voltages and apply AC-coupled feedforward, decoupling the amplifier and power stages, and using high-pass and low-pass filtering to generate driving signals with appropriate DC voltages and AC swings, thereby reducing quiescent current while maintaining linearity.

Engineering Contradictions & Design Principles

VSEngineering 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

Engineering Contradiction:

Improvequiescent currentVSAvoidlinearity

Core Design Contradiction:

Use of energy by moving objectVSManufacturing precision

Solution Approach 1:

The invention segments the direct coupling between amplifier stage and power stage by introducing a DC-shifting stage. This intermediate stage separates the DC biasing functions from the AC signal transmission, allowing the amplifier stage to operate with optimal linearity while the power stage uses small gate-source voltages for low quiescent current. The DC-shifting stage processes each signal path independently, enabling precise control of DC levels without affecting AC signal integrity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The DC-shifting stage acts as an intermediary between the amplifier stage and power stage. It receives signals from the amplifier stage, adjusts their DC voltage levels through controlled voltage shifting, and delivers the adjusted signals to the power stage. This intermediary function allows the two stages to operate independently with optimized parameters - the amplifier stage maintains high linearity while the power stage achieves low quiescent current through small gate-source voltages.

Inventive Principle:

Principle #24Intermediary (Mediator)

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

Engineering Contradiction:

Improvequiescent currentVSAvoidoutput signal swings

Core Design Contradiction:

Use of energy by moving objectVSPower

Solution Approach 1:

The DC-shifting stage segments the signal processing functions, allowing AC signal swings to be preserved through the stage while DC voltage levels are independently adjusted. This segmentation enables the power stage to receive signals with sufficient AC swing amplitude even when operating with small gate-source voltages, thereby maintaining output power capability while reducing quiescent current.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The DC-shifting stage dynamically adjusts DC voltage parameters of the signals without affecting AC signal swing parameters. By changing only the DC offset parameter while preserving AC amplitude and frequency characteristics, the system enables the power stage to operate with small gate-source voltages for low quiescent current while maintaining adequate output signal swings through proper DC level positioning.

Inventive Principle:

Principle #35Parameter changes

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The solution achieves good linearity with low quiescent current by preserving AC signals and optimizing DC voltages, enhancing the performance of the linear amplifier.

Implementation Method 1

the compensation network performs a high-pass filtering operation on the first signal, performs a low-pass filtering operation on the adjusted first signal, and combines a high-pass filtering result of the first signal and a low-pass filtering result of the adjusted first signal to generate the first driving signal

Methodology Applied

Scientific EffectHigh-pass filtering: Filter (electronic)

Implementation Method 2

Methodology Applied

Scientific EffectLow-pass filtering: Filter (electronic)

Data Source

PatentEP4148992B1Amplifier output stage with DC-shifting circuit for high-speed supply modulator

Publication Date: 2025.12.24 MEDIATEK INC

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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.