Doherty Amplifier Bias Control for Stable RF Phase Characteristics
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Solution Overview
Problem
Doherty amplifier circuits face issues with changes in transmission phase characteristics due to bias point adjustments in common-emitter amplifiers, leading to distortion in radio-frequency output signals, and existing bias circuits struggle to control bias points effectively, especially with high input voltages.
Innovation Solution
A Doherty amplifier circuit design that includes variable-gain amplifiers with a current draw circuit, utilizing a first transistor and a control signal to manage the bias point and gain of amplifiers, thereby suppressing changes in input impedance and phase characteristics, and incorporating a current draw circuit to control emitter current and reduce power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the bias point of a common-emitter amplifier is changed to control gain, then the gain of the peaking amplifier can be adjusted, but the input impedance and transmission phase characteristics change significantly, causing distortion in the radio-frequency output signal
Solution Approach 1:
The amplifier is divided into two independent parts: a common-emitter amplifier for gain control and a common-collector amplifier for impedance buffering. This segmentation allows the common-emitter stage to adjust gain while the common-collector stage maintains stable input impedance and phase characteristics, resolving the contradiction between gain adaptability and transmission reliability
Solution Approach 2:
The common-collector amplifier acts as an intermediary between the common-emitter amplifier and the load. It buffers the output of the common-emitter stage, preventing impedance and phase variations from affecting the overall transmission characteristics, thus maintaining signal integrity while allowing gain adjustment
2Reliability
If a typical bias circuit is used to determine the bias point, then the bias point can be established, but the circuit requires a high input voltage (about twice the threshold voltage), making it difficult to add control signals
Solution Approach 1:
The bias circuit uses a voltage divider with adjustable resistors that can be dynamically controlled by a control signal. This allows the bias point to be adjusted without requiring high input voltages, enabling easy addition of control signals while maintaining bias stability through the voltage division mechanism
Solution Approach 2:
The bias circuit parameters (resistor values in the voltage divider) are made variable through control signals. By changing these parameters dynamically, the bias point can be adjusted to appropriate values without requiring high input voltages, thus facilitating control signal addition while maintaining reliable bias establishment
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
The solution effectively controls gain and suppresses changes in input impedance, maintaining high input impedance at high bias points, reducing distortion, and enabling efficient operation under limited power supply conditions, while maintaining phase consistency and reducing the risk of overcurrent damage.
Implementation Method 1
a first transistor that receives, at a base or gate thereof, a first radio frequency signal, and that outputs, from an emitter or source thereof, a second radio frequency signal obtained by amplifying the first radio frequency signal
Implementation Method 2
The current draw circuit draws, from the emitter or source of the first transistor, a current based on a control signal
Data Source
AI summary
A Doherty amplifier circuit includes a carrier amplifier including one or more amplifiers, and a peaking amplifier including one or more amplifiers. At least one of the amplifiers includes a first transistor and a current draw circuit. The first transistor receives, at its base or gate, a first radio frequency signal, and outputs, from its emitter or source, a second radio frequency signal obtained by amplifying the first radio frequency signal. The current draw circuit draws, from the emitter or source of the first transistor, a current based on a control signal.