LNA Second-Harmonic Trap Using Transformer-Capacitor Tuning
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Solution Overview
Problem
In multi-band, multi-standard wireless communication systems, cascode low noise amplifiers (LNAs) face challenges in suppressing second harmonic frequencies caused by interfering signals, leading to interference with desired signals and degrading receiver performance, which current solutions address with additional linearization circuits that increase power consumption and complexity.
Innovation Solution
A low noise amplifier circuit with a second-harmonic trap, comprising a transformer and a variable capacitor, is used to create a high impedance at the second harmonic frequency, effectively acting as an open circuit and reducing intrinsic second-order nonlinearity, thereby suppressing intermodulation and harmonic interference without increasing power consumption or system complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If additional linearization circuits are added to suppress second harmonic frequencies, then interference suppression is improved, but power consumption and system complexity increase
Solution Approach 1:
The patent extracts and targets specifically the second harmonic frequency component using a band-stop filter designed to reject only the second harmonic frequency. This selective extraction approach suppresses the harmful second harmonic interference without requiring complex linearization circuits that would address broader frequency ranges, thereby maintaining system simplicity while achieving effective interference suppression.
Solution Approach 2:
The patent applies local quality by implementing a frequency-selective filter with specific characteristics tailored for second harmonic rejection. The filter is designed with particular impedance values and frequency response characteristics optimized for the second harmonic frequency, providing targeted suppression without affecting other frequency components, thus avoiding the need for complex full-band linearization circuits.
2Object-affected harmful factors
If additional linearization circuits are added to suppress second harmonic frequencies, then interference suppression is improved, but power consumption increases
Solution Approach 1:
The patent extracts and targets specifically the second harmonic frequency component using a band-stop filter designed to reject only the second harmonic frequency. This selective extraction approach suppresses the harmful second harmonic interference without requiring complex linearization circuits that would address broader frequency ranges, thereby maintaining system simplicity while achieving effective interference suppression.
3Reliability
If conventional cascode LNA with inductive source degeneration is used, then noise performance is improved, but second harmonic suppression is insufficient
Solution Approach 1:
The patent merges the conventional cascode LNA structure with an inductive source degeneration network and a band-stop filter. The cascode configuration maintains low noise performance, while the added band-stop filter specifically targets second harmonic frequencies. This combination allows the system to retain the noise performance benefits of the cascode architecture while adding targeted second harmonic suppression capability.
Solution Approach 2:
The patent applies local quality by implementing a frequency-selective filter with specific characteristics tailored for second harmonic rejection. The filter is designed with particular impedance values and frequency response characteristics optimized for the second harmonic frequency, providing targeted suppression without affecting other frequency components, thus avoiding the need for complex full-band linearization circuits.
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 efficiently suppresses second harmonic frequencies, improving receiver sensitivity and performance by reducing intermodulation distortion without adding power consumption or complexity, thus enhancing the overall performance of the receiver chain.
Implementation Method 1
the variable capacitor having an adjustable capacitance. The adjustable capacitance may be adjusted for the second-harmonic trap to act as the open circuit at the second harmonic frequency
Data Source
AI summary
An amplifier circuit for amplifying an input signal includes a transistor configured to receive the input voltage via an input port, and a second-harmonic trap connected between the transistor and ground, the second-harmonic trap having an impedance high enough to enable the second-harmonic trap to act as an open circuit at a second harmonic frequency of a voltage provided by the transistor. The second-harmonic trap includes a transformer including a primary winding connected to ground and a secondary winding, the primary winding receiving the voltage provided by the transistor. The second-harmonic trap further includes a variable capacitor connected in parallel with the secondary winding of the transformer, the variable capacitor having an adjustable capacitance that may be adjusted for the second-harmonic trap to act as the open circuit at the second harmonic frequency.