Transformer Notch Filter for Second-Order Harmonic Suppression
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Solution Overview
Problem
Current RF transmitter designs face challenges in suppressing second-order harmonics without incurring significant signal loss or increasing the Bill Of Materials (BOM) cost and physical form factor, particularly in low-cost and low-power IoT applications.
Innovation Solution
A compact notch filter integrated into a semiconductor die, comprising a filter transformer with overlapping windings and a variable capacitor bank, which presents a capacitive load to differential signals and a series-resonant inductive-capacitive load to common-mode signals, effectively suppressing second-order harmonics while minimizing signal loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If an external filter is used to suppress the second order harmonic, then the emission limit is met, but the BOM cost and physical form factor increase
Solution Approach 1:
The patent merges the harmonic suppression function with the existing RF output port structure by integrating an LC series resonator directly at the output port. This combines multiple functions (signal output and harmonic filtering) into a single integrated structure, eliminating the need for separate external filters and reducing both BOM cost and physical form factor while maintaining effective second order harmonic suppression
Solution Approach 2:
The patent introduces an LC series resonator as an intermediary element at the RF output port that selectively targets and suppresses the second order harmonic frequency. This intermediary component acts as a frequency-specific mediator that blocks harmful harmonics while allowing the fundamental carrier signal to pass through, achieving harmonic suppression without requiring complex external filtering structures
2Device complexity
If an LC series resonator is used as an internal filter on the RF output port, then the BOM cost and physical form factor are reduced, but the fundamental tone suffers from severe signal loss
Solution Approach 1:
The patent applies local quality by designing the LC series resonator with specific component values and characteristics tailored to target only the second order harmonic frequency. The inductor and capacitor are selected to create a resonant condition specifically at the harmonic frequency, ensuring that the filtering effect is localized to the harmful frequency while the fundamental tone passes through with minimal attenuation
Solution Approach 2:
The patent utilizes parameter changes by adjusting the inductance and capacitance values of the LC series resonator to achieve frequency-selective filtering. By carefully selecting component parameters, the resonator is tuned to resonate at the second order harmonic frequency, creating a high-impedance path for the harmonic while maintaining a low-impedance path for the fundamental carrier signal, thus minimizing signal loss
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 achieves efficient suppression of second-order harmonics, meeting emission limits without degrading the desired output signal, and is cost-effective and compact, suitable for modern IoT applications.
Implementation Method 1
a filter transformer including a first winding and a second winding
Implementation Method 2
An inductive-capacitive (LC) series resonator on the RF output port as an internal filter in the transceiver IC may also be used to suppress the second order harmonic
Data Source
AI summary
A notch filter is coupled to a first input node and a second input node, and is configured to present a capacitive load to a differential signal provided to the first and second input nodes, and to present a series-resonant inductive-capacitive load to a common-mode signal provided to the first and second input nodes. The notch filter includes a transformer and a capacitor bank. The transformer includes a first winding having a positive-polarity terminal coupled to the first input node and a second winding having a positive-polarity terminal coupled to the second input node. The capacitor bank includes a first capacitor coupled between a negative-polarity terminal of the first winding and a bias node, and a second capacitor coupled between a negative-polarity terminal of the second winding and the bias node. The first and second capacitors may be variable capacitors.