RF Filter Circuit With Active AC Shunt for Harmonic Attenuation
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Solution Overview
Problem
Current RF filters in telecommunications devices are bulky and consume significant space, making them unsuitable for smaller devices like WLAN and Bluetooth transceivers, and alternative solutions that eliminate filters require complex and costly signal sources with high power consumption.
Innovation Solution
A compact filter circuit comprising an input terminal, a filter device with resonant circuits, and an active AC shunt circuit that attenuates specific frequencies, efficiently shunting second harmonics to ground while allowing desired frequencies to pass through, using transconductance amplifiers and load resistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional RF filters are used to attenuate out-of-band signals and harmonics, then signal filtering performance is improved, but device size and circuit board area increase significantly
Solution Approach 1:
The filter function is segmented into two distinct parts: a passive filter device for attenuating signals at a given frequency (fundamental frequency), and an active AC shunt circuit for attenuating signals at other frequencies (harmonics). This segmentation allows each part to be optimized independently and implemented with smaller components, reducing overall circuit board area while maintaining effective filtering performance for both fundamental and harmonic frequencies.
Solution Approach 2:
The invention merges the filtering of fundamental frequency signals and harmonic signals into a single integrated circuit structure. The passive filter device and active AC shunt circuit are combined in parallel between the input and output, creating a compact dual-function filter that handles both fundamental and harmonic attenuation in one unit, thereby reducing total device size compared to separate filter implementations.
2Device complexity
If filters are eliminated and high linearity signal sources are used instead, then device complexity is reduced, but power consumption and cost increase
Solution Approach 1:
Instead of requiring a perfectly linear signal source that would eliminate the need for any filtering, the invention uses a practical signal source with acceptable linearity and supplements it with targeted filtering only where needed. The passive filter device and active AC shunt circuit provide selective attenuation of specific frequency components (fundamental and harmonics) rather than requiring complete elimination of all non-idealities, thus maintaining lower power consumption and cost while achieving sufficient signal quality.
Solution Approach 2:
The invention introduces an active AC shunt circuit as an intermediary element between the signal source and output. This active circuit acts as a mediator that selectively shunts harmonic frequencies to ground while allowing the fundamental frequency to pass through, thereby improving signal quality without requiring the signal source itself to be highly complex or power-consuming.
3Reliability
If conventional filters are used to attenuate harmonics, then signal quality is improved, but the filters occupy significant package volume
Solution Approach 1:
The invention transitions from traditional bulky parallel LC resonator implementations to a planar microstrip resonator design that utilizes the circuit board plane as the resonating structure. This dimensional change allows the filter functionality to be implemented in a two-dimensional planar format rather than requiring three-dimensional bulky components, significantly reducing package volume while maintaining effective harmonic attenuation and signal quality.
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 strong attenuation of second harmonics with minimal impact on the first harmonic, reducing device size and complexity, allowing for smaller transceivers with efficient and cost-effective filtering.
Implementation Method 1
The filter device is connected to a second input terminal of the shunt circuit, and is provided for attenuating or blocking the radio frequency signal at a given frequency
Implementation Method 2
The shunt circuit comprises a transconductance or transimpedance amplifier and a load resistor
Data Source
AI summary
A circuit for filtering a radio frequency signal at a given frequency comprises an input terminal, a filter device, and an active AC shunt circuit having first and second input terminals and an output terminal, where the first input terminal of the active AC shunt circuit is connected to the input terminal. The filter device is connected between the input terminal and the second input terminal of the active AC shunt circuit, and is provided for attenuating the radio frequency signal at the given frequency to the second input terminal of the active AC shunt circuit. The active AC shunt circuit is provided for shunting a signal at a frequency other than the given frequency as contained in the radio frequency signal to ground, and for outputting the radio frequency signal as filtered at its output terminal.