Power Amplifier Bias Circuit Using Capacitive Negative Current Bypass
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Solution Overview
Problem
The linearity of gain in power amplification modules is degraded due to the cutting of negative bias current, which is exacerbated by reducing the current supply or increasing the size of transistors, leading to increased current consumption and difficulty in controlling gain.
Innovation Solution
A power amplification module with a bias circuit that includes a first bipolar transistor with a diode-connected configuration, a second bipolar transistor, a third bipolar transistor connected to a resistor, and a capacitor between the base and emitter of the third transistor, allowing the bias current to bypass negative current and maintain linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the current supply Ibias is reduced to improve power efficiency, then current consumption decreases, but the linearity of gain degrades due to negative bias current cutting
Solution Approach 1:
A capacitor is introduced as an intermediary element connected to the bias circuit. This capacitor absorbs and releases charge to prevent the cutting of negative bias current, thereby maintaining linearity of gain while allowing the use of reduced current supply for power efficiency.
Solution Approach 2:
The invention changes the electrical parameters of the bias circuit by adding a capacitor, which alters the time-dependent behavior of the bias current. This parameter change allows the circuit to maintain proper biasing conditions even when the average current supply is reduced, preventing gain linearity degradation.
2Reliability
If the size of transistors Q2 and Q3 is increased to suppress negative bias current cutting, then linearity of gain is improved, but current consumption increases
Solution Approach 1:
The capacitor acts as a mediator that enables the bias circuit to function correctly with smaller transistor sizes. By storing and releasing charge, the capacitor prevents negative current cutting without requiring larger transistors, thus avoiding increased current consumption.
Solution Approach 2:
The invention introduces dynamic behavior through the capacitor, which actively manages the bias current waveform. This dynamic approach allows smaller transistor sizes to be used while maintaining linearity, as the capacitor compensates for the reduced current handling capability of smaller devices.
3Adaptability or versatility
If the current supply Ibias is reduced to enable variable gain control, then gain adaptability is improved, but linearity degradation becomes significant when reducing gain
Solution Approach 1:
The capacitor serves as a mediator that enables variable gain control to be implemented without significant linearity degradation. By preventing negative bias current cutting across different gain settings, the capacitor ensures that linearity is maintained even when the current supply is reduced for gain control.
Solution Approach 2:
The capacitor enables periodic charge and discharge cycles that maintain proper biasing conditions during variable gain control. This periodic action ensures that negative current cutting is prevented across the full range of gain settings, maintaining linearity while enabling gain adaptability.
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 suppresses the degradation of linearity in the power amplification module by preventing the cutting of negative bias current, thereby maintaining gain control while reducing current consumption.
Implementation Method 1
a first capacitor that is provided between the base and the emitter of the third bipolar transistor
Data Source
AI summary
A power amplification module includes a first amplification transistor that receives a first signal outputs an amplified second signal from the collector thereof; and a bias circuit that supplies a bias current to the base of the first amplification transistor. The first bias circuit includes a first transistor that is diode connected and is supplied with a bias control current; a second transistor that is diode connected, the collector thereof being connected to the emitter of the first transistor; a third transistor, the base thereof being connected to the base of the first transistor, and the bias current being output from the emitter thereof; a fourth transistor, the collector thereof being connected to the emitter of the third transistor and the base thereof being connected to the base of the second transistor; and a first capacitor between the base and the emitter of the third transistor.