Transformer-Coupled Amplifier Circuit for Low-Frequency Impedance Control
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Solution Overview
Problem
The existing amplifier circuits face issues with increased impedance in the low frequency band, leading to a deterioration in Adjacent Channel Leakage Power Ratio (ACLR) due to the memory effect when the LC series resonance circuit is added.
Innovation Solution
The proposed amplifier circuit includes a high frequency input terminal and output terminal, first and second amplifying elements, an output transformer, first and second inductors, and a first bypass capacitor. The output ends of the amplifying elements are connected to the input and output coils of the transformer, with the inductors and bypass capacitor configured to reduce impedance in the low frequency band.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If an LC series resonance circuit is added to suppress high frequency noise, then power supply voltage or bias voltage with suppressed high frequency noise is achieved, but impedance in low frequency band increases causing memory effect and ACLR deterioration
Solution Approach 1:
The patent divides the noise suppression function into separate frequency bands by using multiple parallel resonance circuits with different resonant frequencies. One circuit targets high frequency noise while another targets low frequency impedance reduction, allowing independent optimization of each frequency band's performance without mutual interference
Solution Approach 2:
The patent nests multiple resonance circuits within the same power supply or bias voltage line by connecting them in parallel. Each resonance circuit is embedded within the same electrical path, with each circuit containing its own LC series combination, creating a nested structure where multiple frequency-specific filtering functions coexist in the same voltage supply path
2Object-affected harmful factors
If bypass capacitor is added between power supply voltage supply terminal and ground, then high frequency noise is suppressed, but impedance in low frequency band increases
Solution Approach 1:
The patent makes the power supply voltage line serve multiple functions simultaneously: it provides power supply voltage to the amplifying elements, suppresses high frequency noise through the bypass capacitor, and reduces low frequency impedance through the parallel resonance circuit. This multi-functional design eliminates the need for separate circuits for each function
Solution Approach 2:
The patent changes the impedance parameter of the power supply line across different frequency bands by introducing resonant circuits with specific resonant frequencies. The impedance is reduced at low frequencies through resonance while maintaining high frequency noise suppression, achieving frequency-dependent impedance optimization
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 configuration effectively reduces impedance in the low frequency band, thereby improving the ACLR and suppressing the memory effect in the amplifier circuit.
Implementation Method 1
by adding the LC series resonance circuit disclosed in Patent Document 2
Data Source
AI summary
An amplifier circuit includes a high frequency input terminal and a high frequency output terminal, amplifiers, an output transformer having an input-side coil and an output-side coil, inductors, and a bypass capacitor. An output end of the amplifier is connected to one end of the input-side coil and one end of the inductor. An output end of the amplifier is connected to the other end of the input-side coil and one end of the inductor. The other end of the inductor, the other end of the inductor, and one end of the bypass capacitor are connected to a midpoint of the input-side coil. One end of the output-side coil is connected to the high frequency output terminal.