RF Power Amplifier Transformer Feedback for Injection Pulling Mitigation
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Solution Overview
Problem
Conventional RF transmitter circuits, particularly those with digitally controlled oscillators (DCO) and digital power amplifiers (DPA), suffer from efficiency losses due to harmonic distortion and injection pulling, which limit their performance and power efficiency, especially at low supply voltages.
Innovation Solution
The implementation of a feedback capacitor and a matching network transformer in an inverting configuration, along with a magnetically coupled coil, to suppress harmonic distortion and mitigate injection pulling by enhancing feedback coupling and controlling the magnetic coupling factor between the DCO and DPA.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a digital power amplifier (DPA) is used to reduce supply voltage and power, then power consumption is reduced, but harmonic distortion occurs at frequencies similar to the DCO operating frequency causing injection pulling
Solution Approach 1:
The patent converts the harmful harmonic distortion generated by the DPA into a beneficial feedback signal. By tapping the harmonic distortion at the DPA output and feeding it back through a feedback network (including feedback capacitor Cfb and inductor Lfb) to the DCO, the harmful distortion is transformed into a control signal that adjusts the DCO frequency to compensate for injection pulling, thereby converting the harmful effect into a useful frequency correction mechanism
Solution Approach 2:
The patent implements a feedback mechanism where the harmonic distortion signal from the DPA is captured and fed back to the DCO through a feedback network. The feedback signal is processed through capacitors and inductors to generate a correction signal that adjusts the DCO operating frequency, creating a closed-loop system that automatically compensates for injection pulling effects caused by the DPA's harmonic distortion
2Loss of energy
If the DPA operates at low supply voltage to improve efficiency, then power efficiency is improved, but injection pulling occurs at the DCO
Solution Approach 1:
The patent employs a feedback loop that captures harmonic distortion from the DPA output and feeds it back to the DCO through a network containing feedback capacitor Cfb and inductor Lfb. This feedback mechanism generates a correction signal that stabilizes the DCO frequency against injection pulling, maintaining frequency stability even when the DPA operates at low supply voltage for improved efficiency
Solution Approach 2:
The patent changes the operating parameters of the feedback network (capacitor Cfb, inductor Lfb, and resistor Rfb values) to optimize the feedback signal characteristics. By adjusting these parameters, the system can maintain effective frequency stabilization across different supply voltages, allowing the DPA to operate efficiently at low voltage while preserving DCO frequency 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
This solution effectively reduces injection pulling, enhances power amplifier efficiency, and allows the RF circuit to operate efficiently at low supply voltages while minimizing harmonic distortion, thereby improving the overall performance of the RF transmitter.
Implementation Method 1
The capacitor is electrically coupled between a primary winding and a secondary winding of the matching network transformer. Serving as a feedback capacitor, the capacitor can enhance a feedback coupling from the secondary winding to the primary winding
Implementation Method 2
The oscillator comprises a coil magnetically coupled between the primary winding and the secondary winding of the power amplifier to sense the coupling of the power amplifier to send an amplified but inverted signal back to the windings
Data Source
AI summary
Systems and methods for suppressing and mitigating harmonic distortion in a circuit are disclosed. In one example, a disclosed circuit includes a radio frequency (RF) oscillator and a power amplifier. The RF oscillator is configured to generate an RF signal. The power amplifier is configured to generate an amplified RF signal based on the RF signal. The power amplifier includes a transformer including a primary winding and a secondary winding, and a feedback capacitor electrically coupled to the primary winding and the secondary winding.