RF Amplifier Bias Circuit With Variable Impedance for Linearity
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing amplifier circuits face challenges in adjusting the bias current to maintain appropriate linearity due to fixed inductance values, which are affected by variations in amplifying transistors and environmental changes, leading to degradation in transistor linearity.
Innovation Solution
The proposed amplifier circuit incorporates a variable resistance circuit connected in series with an inductor between the emitter or source of an emitter-follower/source-follower circuit and the control terminal of the amplifier transistor, allowing for adjustable impedance to maintain constant gain and improved linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed inductance value is used in the biasing inductor, then the circuit structure is simple, but the bias current cannot be adjusted appropriately due to transistor variations and environmental changes, causing degradation in linearity
Solution Approach 1:
The patent applies the Dynamics principle by replacing the fixed inductance value with a variable inductance that can be adjusted according to transistor variations and environmental changes. This allows the bias current to be dynamically tuned to maintain appropriate linearity performance under different operating conditions, resolving the contradiction between simple structure and reliable performance.
Solution Approach 2:
The patent applies the Parameter changes principle by changing the inductance value parameter of the biasing inductor from a fixed value to a variable value. This enables adjustment of the bias current magnitude to compensate for transistor variations and environmental effects, thereby maintaining linearity without significantly complicating the overall circuit structure.
2Reliability
If the bias current is adjusted to compensate for transistor variations, then linearity improves, but the circuit complexity increases due to additional adjustment mechanisms
Solution Approach 1:
The patent uses parameter changes by adjusting the inductance value of the biasing inductor to control the bias current magnitude. This provides a straightforward method to improve linearity without introducing complex adjustment mechanisms, as the inductance parameter can be varied through simple design modifications rather than complex control circuits.
Solution Approach 2:
The patent applies universality by designing the biasing inductor to serve multiple functions: it provides the necessary bias current blocking while also enabling bias current adjustment through variable inductance. This multi-functionality allows linearity improvement without adding separate adjustment circuits, thereby avoiding excessive complexity.
3Reliability
If a variable resistance circuit is added to the inductor, then gain constancy and linearity are maintained across varying output powers, but the device complexity increases
Solution Approach 1:
The patent applies merging by combining the variable resistance circuit with the inductor to form an integrated impedance adjustment mechanism. This combined structure allows simultaneous control of resistance and inductance to maintain gain constancy and linearity across varying output powers, while reducing overall complexity compared to having separate adjustment circuits for each parameter.
Solution Approach 2:
The patent uses universality by designing the variable resistance circuit connected to the inductor to perform multiple functions: it adjusts the impedance to maintain gain constancy, controls bias current for linearity, and operates across varying output powers. This multi-functionality reduces the need for separate control circuits, thereby limiting the increase in device complexity.
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
This configuration enables the amplifier circuit to maintain constant gain and reduce distortion across varying output powers, enhancing linearity and suppressing thermal runaway, thereby improving the performance of the amplifier circuit.
Implementation Method 1
an inductor arranged in series between an emitter of the emitter-follower circuit and the control terminal or between a source of the source-follower circuit and the control terminal
Implementation Method 2
a variable resistance circuit connected to the inductor
Data Source
AI summary
An amplifier circuit includes an input terminal to which a radio frequency signal is input, an amplifier transistor that has a control terminal and amplifies the radio frequency signal, a bias circuit that includes an emitter-follower circuit or a source-follower circuit and supplies a bias current to the control terminal of the amplifier transistor, an inductor arranged in series between an emitter of the emitter-follower circuit and the control terminal of the amplifier transistor or between a source of the source-follower circuit and the control terminal of the amplifier transistor, and a variable resistance circuit connected to the inductor.