Variable Gain Power Amplifier with Current-Based Gain Control
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Solution Overview
Problem
Conventional variable gain power amplifiers experience significant gain fluctuations due to slight changes in control voltage, making it difficult to achieve desired gain accuracy, especially in compact IC-based transmitters for ISM band and RKE applications.
Innovation Solution
A variable gain power amplifier design incorporating a signal generating unit with a switching circuit, constant current source, and variable current source, where the control signal magnitude depends on the sum of these currents, allowing precise analog control of power gain through a control terminal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a variable current source is applied to the base of the power amplifying transistor to control gain through shunt control of base bias current, then the amplifier can be controlled by a simple circuit configuration, but a slight fluctuation in control voltage leads to a large fluctuation in gain, impeding attainment of desired gain with high accuracy
Solution Approach 1:
The patent changes the control parameter from voltage to current. Instead of applying control voltage to a variable current source that controls base bias current, the invention directly applies a control current to the base of the power amplifying transistor. This current control approach provides more precise gain control because current has a more direct and linear relationship with the transistor's operating point, reducing the sensitivity to control signal fluctuations and improving gain control accuracy.
2Adaptability or versatility
If gain control is performed through controlling the base current depending on the control voltage, then the amplifier can be adjusted for different gain levels, but the gain control becomes highly sensitive to voltage fluctuations, reducing control precision
Solution Approach 1:
The patent substitutes voltage control with current control. By replacing the voltage-dependent variable current source configuration with a direct current control approach, the system achieves more precise and stable gain control. The control current directly modulates the base current of the power amplifying transistor, creating a more accurate and less sensitive control mechanism compared to voltage-based control.
Data Source
AI summary
A variable gain power amplifier includes a power amplifying unit and a signal generating unit. The power amplifying unit includes a control terminal, and a gain of the power amplifying unit is variable by a control signal provided through the control terminal. The signal generating unit generates the control signal to be provided to the control terminal. The signal generating unit includes a switching circuit to be turned on and off by a binary signal, a constant current source that generates a constant current, and a variable current source that generates a variable current. Also, the signal generating unit generates, when the switching circuit is on, a control signal of a magnitude that turns on the power amplifying unit and depends on a magnitude of a sum of the constant current and the variable current. When the switching circuit is off, the signal generating unit generates a control signal of a magnitude that turns off the power amplifying unit.