N-Path RF Quadrature Circuit With Frequency-Selective Filtering
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Solution Overview
Problem
Existing IQ generators and combiners at RF frequencies suffer from lack of frequency selectivity, sensitivity to blockers, bulkiness, and 3dB path losses, limiting their performance and flexibility.
Innovation Solution
An N-path filter (NPF) architecture using switched capacitors with a 1/N duty cycle generates or combines quadrature signals, reducing losses to approximately 1.8dB per path and providing high quality factor frequency filtering without resistance or inductance, enabling compact design and frequency agility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If polyphase filter architectures are used to generate quadrature signals, then the device can perform IQ generation, but the device becomes bulky and suffers from 3dB path losses
Solution Approach 1:
The patent replaces traditional polyphase filter architectures with an N-path filter architecture that uses switched capacitors instead of resistors and inductors. This substitution reduces path losses from 3dB to approximately 1.8dB per path while achieving a more compact design through the use of integration capacitors and switch-based signal routing.
2Reliability
If traditional IQ generators are used, then quadrature signals can be generated, but frequency selectivity is poor making receivers sensitive to blockers
Solution Approach 1:
The patent implements frequency-selective filtering through the N-path filter architecture where the transfer function varies with frequency. The switched capacitor network provides frequency-dependent signal routing and filtering, enabling the receiver to selectively pass desired frequencies while rejecting blockers, thereby improving reliability without sacrificing adaptability.
3Adaptability or versatility
If polyphase filters are used for quadrature signal generation, then the basic function is achieved, but the device lacks frequency agility
Solution Approach 1:
The N-path filter architecture serves multiple functions: it generates quadrature signals, provides frequency-selective filtering, and enables frequency-agile operation. The same switched capacitor network that creates the quadrature outputs also inherently provides the frequency-selective behavior, eliminating the need for separate filtering components and achieving multi-functionality in a unified structure.
Data Source
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AI summary
Radio Frequency Device (10) of NPF type comprising a first end terminal E1, four first branches named BR10, BR11, BR12, BR13 connected to E1 and each comprising: - a capacitor, respectively C0, C1, C2, C3, of the same capacitance, comprising a first terminal and a second terminal connected to ground, and - a switch arranged between E1 and the first terminal of the capacitor of said first branch; said device (10) being adapted to, in each first branch BR1i, close the switch at each instant pT0 + (i) T0/4, during T0/4, with p natural integer and T0 period of the clock signal;the device comprising at least two successive second branches from an ordered set of second branches BR20, BR21, BR22, BR23, the second branch BR2i comprising a second end terminal E2i, and each second branch of the device BR2k comprising, for each first branch, BR1i, i = 0 to 3, a switch between the first terminal of the capacitor Ci and said second branch, said device being adapted to close said switch at each pT0 + (i + k) T0/4, during T0/4.;