Tunable N-Path Notch Filter for Out-of-Band Noise Rejection
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Solution Overview
Problem
Existing communication receivers face interference from unwanted signals, particularly in densely congested wireless spectra, where off-chip filters are costly and bulky, and coexistence of different wireless protocols in hand-held devices leads to performance degradation due to out-of-band noise leakage.
Innovation Solution
A shunt N-path notch filter with tunable center frequency, using a series inductor and capacitor that can be bypassed for band-pass operation, and controlled by clock pulses to achieve linear, high quality factor filtering without the need for bulky off-chip filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If off-chip filters (SAW/BAW) are used to reduce out-of-band noise, then noise filtering performance is improved, but device cost and form factor increase
Solution Approach 1:
The patent replaces mechanical/off-chip filter systems (SAW/BAW filters requiring physical mounting) with an integrated electronic N-path filter circuit that can be fabricated directly on the chip using standard CMOS processes, thereby eliminating the need for bulky off-chip components while maintaining noise filtering functionality
Solution Approach 2:
The N-path filter circuit is designed to be universally applicable across different frequency bands and protocols by tuning the switching frequency and RC time constants, allowing a single integrated circuit to serve multiple filtering functions that would traditionally require separate off-chip filters for different applications
2Object-affected harmful factors
If off-chip filters (SAW/BAW) are used to reduce out-of-band noise, then noise filtering performance is improved, but device cost increases
Solution Approach 1:
The patent replaces expensive off-chip filter components with an integrated electronic N-path filter circuit that utilizes standard CMOS process components (switches, capacitors, resistors), thereby eliminating the need for costly specialized filter manufacturing and assembly processes
Solution Approach 2:
The patent employs inexpensive standard CMOS process components (metal-insulator-metal capacitors, poly-silicon resistors, MOS switches) that can be mass-produced using existing semiconductor fabrication processes, replacing expensive specialized off-chip filter components with cheap, readily available integrated circuit elements
3Object-affected harmful factors
If baseband filtering is used to reduce noise, then noise reduction is achieved, but complexity of amplification stages increases
Solution Approach 1:
The patent performs noise filtering at the RF stage before the signal undergoes amplification and downconversion to baseband, thereby preventing noise from being amplified by subsequent stages rather than requiring complex noise reduction processing after amplification occurs
Solution Approach 2:
The patent replaces complex baseband digital signal processing required for noise reduction with a simple analog N-path filter circuit operating at RF, thereby reducing the computational complexity and processing requirements of baseband amplification and filtering stages
4Productivity
If active-mixers are used in frequency-division duplexing systems, then signal processing capability is improved, but noise and non-linearity contributions increase
Solution Approach 1:
The patent performs noise filtering at the RF input stage before the signal enters active-mixers and other non-linear processing stages, thereby preventing out-of-band noise from being converted to in-band noise through inter-modulation and spurious mixing that occurs in active-mixers
Solution Approach 2:
The patent applies preliminary filtering to counteract the harmful effects of active-mixers by removing out-of-band noise and spurious signals before they can undergo non-linear mixing processes, thereby preventing the generation of in-band noise and distortion products that would otherwise degrade signal quality
Data Source
AI summary
A linear, low noise, high quality factor (Q) and widely tunable notch filter circuit includes one or more first reactive elements coupled between a first filter node and a first node. The notch filter circuit further includes a multi-branch circuit having multiple parallel branches and coupled between the first node and a second node. Each branch of the multi-branch circuit includes at least a switch coupled to a variable capacitor. A notch frequency of the notch filter circuit is tunable by adjusting a capacitance of the variable capacitor.