Dynamic Bias Circuit for Power Amplifier Linearity and Efficiency
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Solution Overview
Problem
Power amplification circuits face inefficiencies in current consumption during small power output due to constant current flow in bias circuits, leading to decreased power addition efficiency and linearity degradation from gain expansion at intermediate power outputs.
Innovation Solution
A power amplification circuit design that includes a control voltage generating circuit to adjust the bias current or voltage based on signal levels, using a first transistor, a second transistor between its emitter/source and ground, and a third transistor with control voltage supplied to its base/gate, reducing current consumption at small power outputs while suppressing gain expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a constant current source transistor is always in an on state to suppress gain expansion at intermediate power output, then linearity is improved, but current consumption increases at small signal input
Solution Approach 1:
The bias circuit dynamically adjusts the bias current based on the amplitude of the high-frequency signal. When the signal amplitude is large (intermediate power output), the bias current is increased to suppress gain expansion and maintain linearity. When the signal amplitude is small, the bias current is decreased to reduce power consumption. This dynamic adjustment resolves the contradiction between maintaining linearity and reducing current consumption.
Solution Approach 2:
The invention changes the parameter of bias current from a constant value to a variable value that depends on the signal amplitude. By monitoring the amplitude of the high-frequency signal and adjusting the bias current accordingly, the system achieves optimal linearity only when needed (at intermediate power output) while minimizing current consumption at small signal input.
2Reliability
If bias current is increased to suppress gain expansion at intermediate power output, then linearity is improved, but power addition efficiency decreases at small power output
Solution Approach 1:
The bias circuit transitions from a static constant current source to a dynamic current source that responds to signal amplitude. At small power output, the bias current is reduced to minimize its impact on power addition efficiency. At intermediate power output, the bias current is increased to suppress gain expansion and improve linearity. This dynamic behavior resolves the contradiction between linearity and power addition efficiency.
Solution Approach 2:
The invention changes the bias current parameter from fixed to variable, allowing the system to optimize power addition efficiency at small power output by reducing bias current, while maintaining linearity at intermediate power output by increasing bias current when needed.
Data Source
AI summary
A power amplification circuit includes: a first amplifier that is input with a first signal and outputs a second signal; a bias circuit that supplies a bias current or voltage to the first amplifier; and a control voltage generating circuit that generates a control voltage in accordance with the first signal. The bias circuit includes a first transistor that outputs the bias current or voltage, a second transistor provided between the emitter or source of the first transistor and ground, and a third transistor that is supplied with the control voltage and that supplies a first current or voltage to the second transistor. The value of the first current or voltage when the signal level is a first level is larger than the value of the first current or voltage when the signal level is a second level. The first level is higher than the second level.