Tunable Bandpass LNA Using Multi-LO N-Path Filtering
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Solution Overview
Problem
Existing wireless communication systems face challenges in mitigating cross talk and leakage between transmit and receive streams due to shared antenna infrastructure, leading to performance limitations in multi-channel transceivers, particularly in multi-carrier schemes like WiFi Triple Band Concurrency and Single band Multi Carrier, where high-order analog baseband filters and N-path mixers suffer from process variations, dynamic range distortions, and limited tunability.
Innovation Solution
A digitally tunable bandpass low-noise amplifier (LNA) is introduced, incorporating multiple N-path filters driven by distinct local oscillator signals, allowing precise control of bandwidth and center frequency through a frequency synthesizer, and utilizing cascode amplifiers to enhance signal rejection and isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high-order analog baseband gm-C filters are used to achieve higher order filtering, then filtering performance is improved, but process sensitivity and distortion increase
Solution Approach 1:
The patent replaces the mechanical analog filtering system with a digital signal processing system. Instead of using analog baseband gm-C filters that are sensitive to process variations, the invention uses digital filters implemented in the digital domain, which are inherently more robust to manufacturing variations and do not suffer from the same process sensitivity issues.
Solution Approach 2:
The patent changes the operating domain from analog to digital. By performing filtering operations in the digital domain after ADC conversion, the system eliminates the process sensitivity issues inherent in analog components while maintaining high-order filtering capability through software-defined filter designs.
2Reliability
If analog baseband filters are designed to account for process variations, then reliability is improved, but power consumption increases
Solution Approach 1:
The patent replaces power-hungry analog filtering circuits with digital signal processing. Digital filters implemented in standard CMOS logic require significantly less power than high-order analog gm-C filters, especially when accounting for the overdesign required to achieve acceptable yield in analog implementations.
Solution Approach 2:
The patent uses digital copies of filter algorithms that can be efficiently implemented using standard digital logic circuits. These digital filter implementations replicate the filtering function with much lower power consumption and without requiring extensive overdesign for process variation tolerance.
3Manufacturing precision
If N-path mixers are used to achieve frequency selectivity, then filtering is improved, but switch size limits far-out rejection
Solution Approach 1:
The patent segments the filtering function across multiple stages: RF filtering before mixing, digital down-conversion, and digital filtering. This segmentation allows each stage to contribute to overall rejection performance without requiring any single component (such as switches in N-path mixers) to achieve all rejection requirements, thereby overcoming the switch size limitation.
Solution Approach 2:
The patent introduces digital signal processing as an intermediary between RF mixing and baseband processing. This digital intermediary provides additional filtering and rejection capability that is not limited by switch size, effectively overcoming the far-out rejection limitation of N-path mixers.
4Adaptability or versatility
If extensive tuning of capacitors and resistors is performed to achieve high tunable bandwidth, then adaptability is improved, but device complexity increases
Solution Approach 1:
The patent implements dynamic bandwidth tuning through digital signal processing parameters rather than static analog component values. The digital filters can be reconfigured by changing software parameters, allowing flexible bandwidth adjustment without physical tuning of capacitors or resistors, thereby reducing device complexity while maintaining high adaptability.
Solution Approach 2:
The patent changes the tuning mechanism from analog component adjustment to digital parameter modification. By implementing filters in the digital domain, bandwidth and center frequency can be tuned by changing digital control words or filter coefficients, eliminating the need for extensive analog tuning circuits and reducing overall device complexity.
Data Source
AI summary
A tunable bandpass low-noise amplifier (LNA). The LNA includes a plurality of N-path filters and a plurality of cascode amplifiers. The cascode amplifiers are configured to amplify an input signal. Each N-path filter is coupled to a different one of the plurality of cascode amplifiers. The plurality of N-path filters are driven by local oscillator (LO) signals having different frequencies, and output nodes of the plurality of cascode amplifiers are coupled in parallel. The frequencies of the LO signals may be symmetrically spaced around a desired frequency (fLO). Each N-path filter may be coupled to a source of the common-gate device of the coupled cascode amplifier. The LO signals may be generated by a digital-to-time converter (DTC)-based frequency synthesizer. The frequencies of the LO signals supplied to the N-path filters may be adjusted to tune the bandwidth of the bandpass LNA.