Linearized Bias Circuit with Adaptation for Power Amplifier Linearity
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Solution Overview
Problem
Conventional bias circuits for power amplifiers suffer from deteriorating linearity and shifting DC and AC characteristics with increased input signal power and temperature variations, leading to suboptimal communication quality and battery life.
Innovation Solution
A linearized bias circuit with adaptation, comprising a reference voltage source, resistors, and NPN or MOS transistors, provides temperature compensation, linearity improvement, and simultaneous gain and phase compensation by stabilizing the bias current for power amplifiers, especially in Class-AB and Class-B amplification modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional bias circuit is used for power amplifier, then the circuit is simple, but linearity deteriorates with increased input signal power
Solution Approach 1:
The bias circuit is segmented into multiple functional blocks: a reference voltage generation block, a bias current generation block with temperature compensation, and a linearization block. This segmentation allows each block to optimize specific functions while maintaining overall simplicity.
Solution Approach 2:
A reference voltage source and intermediate bias current sources are introduced as mediators between the power amplifier and the bias network. These intermediaries provide stable reference points that improve linearity without significantly increasing circuit complexity.
2Device complexity
If conventional bias circuit is used for power amplifier, then the circuit is simple, but DC and AC characteristics shift with temperature variation
Solution Approach 1:
The bias circuit uses temperature-dependent parameter changes to compensate for temperature effects. Specifically, the bias current is adjusted as a function of temperature through carefully designed resistor-transistor networks that generate compensating voltage drops.
Solution Approach 2:
The circuit exploits thermal effects in reverse - using controlled thermal expansion of voltage drops across resistors and transistors to compensate for the thermal drift of the power amplifier characteristics. The bias network is designed so that its temperature coefficient matches and opposes that of the amplifier.
3Manufacturing precision
If linearized bias circuit is used to improve linearity, then linearity improves, but device complexity increases
Solution Approach 1:
The bias circuit is designed to perform multiple functions simultaneously: providing temperature compensation, improving linearity, and maintaining proper bias levels. This multi-functionality is achieved through a unified circuit architecture rather than separate circuits for each function.
Solution Approach 2:
The linearization function is achieved through self-service mechanisms where the bias circuit automatically adjusts its own parameters based on the operating conditions. The temperature compensation and linearity improvement are automatic functions that do not require external control signals.
4Power
If bias current is increased to improve amplification performance, then amplification performance improves, but DC current consumption increases
Solution Approach 1:
The bias circuit provides dynamic bias current adjustment based on the operating mode. In Class-AB mode, the circuit optimizes the bias current to balance linearity and power consumption, while in Class-B mode, it reduces the bias current to minimize power consumption while maintaining acceptable performance.
Data Source
AI summary
A linearized bias circuit with adaptation resolves the problem happening to the power amplifier with conventional bias circuit that the DC and AC characteristics of the power amplifier shift or even deteriorate due to a temperature variation. The linearized bias circuit with adaptation has a reference voltage source, a first voltage source, a first resistor, a second resistor, a first NPN transistor, a second NPN transistor, and a third NPN transistor. The present invention has the characteristics of bias current temperature compensation, gain and phase compensations to achieve high linearity for the conventional power amplifier and reducing the DC consumption power. At the same time, the quantity of the required elements and layout area in the present invention are small so that the design complexity can be reduced for improving yield, reducing IC layout area, and reducing cost.