N-Path Filter With Fourth-Order Impedance for RF Selectivity
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Solution Overview
Problem
The increasing demand for wireless data rates and spectral efficiency leads to multiple access interference (MAI), cross talk, and leakage in sub-6-GHz communications, causing distortion and increasing bit error and packet error rates.
Innovation Solution
A novel higher-order N-path filter loaded with a fourth-order all-pole driving point impedance is implemented, providing 80 dB/decade radio frequency (RF) selectivity, high linearity, and blocker tolerance, while reducing area requirements and increasing available channels for concurrent communications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional SAW filters are used to provide high selectivity, then filtering performance is improved, but area footprint increases and tunability is lost
Solution Approach 1:
The patent replaces traditional mechanical SAW filter structures with an electronic N-path filter implementation using switched capacitors and operational amplifiers. This substitution allows the same filtering function to be achieved through electronic circuitry rather than acoustic wave mechanisms, enabling tunability and integration while maintaining high selectivity performance
Solution Approach 2:
The N-path filter uses variable capacitors and switched capacitor networks that allow the filtering characteristics to be dynamically adjusted by changing circuit parameters. This enables tunable selectivity and frequency response without requiring physical filter changes, overcoming the non-tunable limitation of SAW filters
2Object-affected harmful factors
If multiple filters are added to handle crowded spectrum, then interference rejection is improved, but device complexity and area increase
Solution Approach 1:
The patent combines multiple filtering functions into a single N-path filter structure that processes multiple frequency channels simultaneously. The multi-path architecture with parallel processing paths allows the filter to handle multiple frequency bands and rejection requirements in one integrated circuit rather than requiring separate filters for each function
Solution Approach 2:
The N-path filter is designed as a universal filtering structure that can reject interference across multiple frequency bands and channels. The same circuit architecture provides both channel selection and interference rejection functions, eliminating the need for separate specialized filters for different interference scenarios
Data Source
Figure 1A~1B
Figure 1C
Figure 1D
AI summary
Embodiments may comprise N-path filter circuitry with tunable radio frequency selectivity and up to 80 decibels per decade roll-off. The N-path filter may comprise at least one input transistor, wherein the at least one input transistor comprises a channel and a gate. A first end of the channel is coupled with a receiver circuitry input, wherein a second end of the channel is coupled with a load. The gate of the at least one input transistor is coupled with a clock circuitry input. The load may comprise a fourth order, all-pole driving point impedance. The impedance may shunt the second end of the channel to a circuit ground or a low voltage circuit rail via the impedance. And the impedance may comprise a first active impedance circuit coupled in series with a second active impedance circuit.