Doherty Power Amplifier Bias Filtering for Harmonic Distortion
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Solution Overview
Problem
Doherty amplifiers suffer from unstable bias current supply to the peak amplifier due to AC components in the detection signal, leading to degradation of output power characteristics such as harmonic distortion.
Innovation Solution
A power amplifier circuit with a Doherty configuration that includes a divider, carrier and peak amplifiers, combiner, and bias circuits, along with a control circuit that uses a detecting unit, output unit, and filter circuit to attenuate AC components in the detection signal, thereby stabilizing the bias current supply to the peak amplifier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the detection signal including AC components is used to control the bias current of the peak amplifier, then the AM-AM characteristics are improved, but the bias current becomes unstable and harmonic distortion increases
Solution Approach 1:
The detection signal is segmented into AC and DC components through a capacitor, allowing the AC components to be separated and removed while retaining the DC component for bias current control. This segmentation resolves the contradiction by enabling AM-AM characteristic improvement through detection while preventing bias current instability by removing AC components.
Solution Approach 2:
The harmful AC components are extracted and removed from the detection signal using a capacitor connected between the detection signal line and ground. This extraction allows the useful DC component to control the bias current stably while eliminating the harmful AC components that caused bias current instability and harmonic distortion.
2Loss of energy
If the carrier amplifier operates at saturation output power level, then the efficiency is increased, but the detection signal includes AC components causing control instability
Solution Approach 1:
A capacitor is introduced as an intermediary element between the detection signal source and the bias current control circuit. This capacitor acts as a mediator that blocks AC components from reaching the control circuit while allowing the DC component to pass through, thus enabling efficient saturated operation while maintaining control stability.
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
Improves AM-AM characteristics and suppresses harmonic distortion by ensuring stable bias current supply to the peak amplifier, enhancing the overall output power characteristics.
Implementation Method 1
a filter circuit that attenuates alternating current (AC) components of the detection signal or AC components of the control signal
Data Source
AI summary
A power amplifier circuit includes a Doherty amplifier including a divider that divides a first signal into a second signal and a third signal, a carrier amplifier that amplifies the second signal and outputs a fourth signal, a peak amplifier that amplifies the third signal and outputs a fifth signal, a combiner that combines the fourth signal and the fifth signal and outputs an amplified signal of the first signal, a first bias circuit that supplies a first bias current or voltage to the carrier amplifier, and a second bias circuit that supplies a second bias current or voltage corresponding to a control signal to the peak amplifier; and a control circuit that supplies the control signal corresponding to a level of the second signal to the second bias circuit. The control circuit includes a detecting unit, an output unit, and a filter circuit.