Power Amplifier Circuit With Harmonic Isolation and Impedance Conversion
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Solution Overview
Problem
Existing power amplifier circuits fail to effectively suppress inter-modulation distortion due to insufficient isolation between the main and secondary paths, especially when the input impedance of the amplifier circuit is low, leading to degradation of linearity.
Innovation Solution
A power amplifier circuit design incorporating an isolation circuit with a second-harmonic attenuation unit and a fundamental attenuation unit, combined with an impedance conversion circuit using a transmission line transformer, to ensure isolation and suppress inter-modulation distortion by deliberately injecting and compensating second harmonic waves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a low-pass filter is used to ensure isolation between the main path and secondary path, then isolation is improved, but when the input impedance of the amplifier circuit is small, the filter fails to attenuate harmonics effectively, resulting in failure to suppress inter-modulation distortion
Solution Approach 1:
The patent introduces an impedance conversion circuit as an intermediary component between the isolation circuit and the amplifier circuit. This transmission line transformer converts the low input impedance of the amplifier circuit to a higher impedance level, enabling the low-pass filter to effectively attenuate second harmonic waves. The intermediary impedance conversion mediator resolves the contradiction by creating conditions where the filter can perform its isolation function properly.
Solution Approach 2:
The patent changes the impedance parameter of the circuit by introducing a transmission line transformer with specific transformation ratio. This parameter change (from low input impedance to higher transformed impedance) enables the low-pass filter to achieve effective attenuation of harmonics, thereby suppressing inter-modulation distortion while maintaining isolation between paths.
2Power
If multiple transistors are connected in parallel to increase output power, then power is improved, but the input impedance of the amplifier circuit decreases
Solution Approach 1:
The transmission line transformer acts as an intermediary impedance conversion device between the parallel transistor amplifier circuit and the isolation circuit. It transforms the low input impedance caused by parallel connection into a higher impedance level, allowing the system to maintain both high output power (through parallel transistors) and adequate input impedance for proper filter operation.
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 design effectively cancels third-order inter-modulation distortions, maintaining linearity by ensuring appropriate isolation between the main and secondary paths, even when the amplifier circuit has low input impedance.
Implementation Method 1
The impedance conversion circuit includes a transmission line transformer. The impedance conversion circuit performs the impedance conversion to make impedance at the input point larger than impedance at the output point.
Implementation Method 2
a second-harmonic attenuation unit which receives a first signal obtained through division of an input signal and which passes a fundamental wave of the first signal and attenuates a second harmonic wave of the first signal
Implementation Method 3
a fundamental attenuation unit which receives a second signal obtained through division of the input signal and which passes a second harmonic wave of the second signal and attenuates a fundamental wave of the second signal
Data Source
AI summary
A power amplifier circuit includes an isolation circuit, an impedance conversion circuit, and an amplifier circuit. The isolation circuit includes a second-harmonic attenuation unit and a fundamental attenuation unit. The second-harmonic attenuation unit, which receives a first signal obtained through division of an input signal, passes fundamental waves of the first signal, and attenuates second harmonic waves of the first signal. The fundamental attenuation unit, which receives a second signal obtained through division of the input signal, passes second harmonic waves of the second signal, and attenuates fundamental waves of the second signal. The isolation circuit outputs, from a combination point, a combined signal obtained by combining the first signal, which has passed through the second-harmonic attenuation unit, with the second signal, which has passed through the fundamental attenuation unit.