Active Harmonic Filter for RF Amplifiers Without External Filters
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Solution Overview
Problem
Conventional RF power amplifiers generate undesirable harmonics due to non-linearity, leading to interference with other wireless systems, and existing harmonic filters, whether on-die or external, face challenges in achieving sufficient rejection levels without increasing die footprint, power consumption, or introducing significant losses.
Innovation Solution
An active harmonic filter is introduced, comprising an operational amplifier with a resistor network and inductive-capacitive elements, which creates a frequency-dependent negative capacitance to define rejection frequency notches, effectively suppressing harmonics by reflecting them back upstream with minimal loss and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If conventional passive harmonic filters (capacitors and inductors) are used to reject harmonic frequencies, then harmonic suppression is achieved, but the die footprint increases and fabrication becomes challenging
Solution Approach 1:
The patent transforms the passive filter approach into an active filter approach by introducing an operational amplifier. This changes the fundamental parameter from passive L/C components to an active circuit with frequency-dependent negative capacitance, enabling harmonic suppression without requiring large physical components that would increase die footprint
Solution Approach 2:
The patent replaces the mechanical/passive filter system (physical inductors and capacitors) with an electronic active filter system using operational amplifiers and frequency-dependent capacitance simulation, eliminating the need for bulky passive components while achieving the same filtering function
2Object-generated harmful factors
If external filter circuits are added to prevent strong harmonic signals, then harmonic rejection is improved, but transmission path losses increase and additional space is required
Solution Approach 1:
The patent merges the filter function directly into the power amplifier by integrating the active filter circuit at the output of the PA. This consolidation eliminates the need for separate external filter circuits, reducing transmission path losses and saving space while maintaining effective harmonic rejection
Solution Approach 2:
The operational amplifier acts as an intermediary element that provides frequency-dependent negative capacitance, enabling the filter function to be achieved without relying on traditional passive L/C components that would introduce additional transmission losses
3Ease of manufacture
If on-die harmonic suppression filters are used, then integration is achieved, but the achievable performance is limited by fabrication constraints
Solution Approach 1:
The patent uses the operational amplifier's frequency-dependent characteristics to simulate negative capacitance, which changes with frequency. This allows the filter performance to be tuned and optimized without being constrained by fixed fabrication parameters of passive components, achieving both integration and high performance
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 active harmonic filter achieves high harmonic suppression with minimal loss and power consumption, meeting stringent spurious emission limits without increasing the die footprint, thus eliminating the need for external filters and reducing costs and transmission path losses.
Implementation Method 1
The filter circuit interface node may have a frequency-dependent negative capacitance corresponding to a low frequency gain of the operational amplifier, half power point bandwidth of the operational amplifier, and output impedance as defined by the resistor network and the first inductive-capacitive element connected thereto
Implementation Method 2
effectively suppressing harmonics by reflecting them back upstream with minimal loss and power consumption
Data Source
AI summary
A radio frequency front end circuit includes an output signal transmission line, an amplifier circuit with an input connected to a radio frequency signal source and an output connected to the output signal transmission line. A harmonic suppression circuit is connected to the amplifier circuit, and includes an active circuit element having a frequency-dependent impedance and is tuned as a reflective trap with a negative capacitance for one or more rejection frequency ranges each corresponding to a multiple of a fundamental frequency of a signal generated by the radio frequency signal source.