RF Front-End Circuit for Wideband Signal Subband Testing
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Solution Overview
Problem
Wideband A/D converters required for RF signal analyzers in 5G and next-generation wireless LANs are expensive and have limited options, making it costly to achieve high accuracy for error vector magnitude (EVM) measurements due to the need for both wideband and high-resolution converters.
Innovation Solution
A front-end circuit that includes a variable frequency oscillator, a first frequency mixer, and a band-pass filter to generate an intermediate frequency signal, which is then filtered to narrow the frequency band for a digitizer, allowing the use of a low-speed but high-accuracy digitizer for testing wideband RF signals by dividing the signal into subbands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a wideband A/D converter is used to test wideband RF signals, then the bandwidth requirement is satisfied, but the cost increases and options are limited
Solution Approach 1:
The patent divides the wideband RF signal into multiple subbands using a bank of band-pass filters, each with a narrow bandwidth. This allows the use of multiple low-speed A/D converters instead of a single wideband converter, reducing cost while maintaining the ability to test wideband signals through parallel processing of subbands
Solution Approach 2:
The patent introduces an intermediary frequency conversion stage that down-converts the wideband RF signal to an intermediate frequency range where it can be processed by multiple narrowband filter banks and low-speed A/D converters, enabling cost-effective wideband signal analysis
2Measurement precision
If a wideband A/D converter is used to achieve high accuracy for EVM measurements, then measurement precision is improved, but the cost increases
Solution Approach 1:
The patent segments the wideband signal into multiple narrow subbands, allowing the use of multiple low-resolution A/D converters for each subband. By processing each subband separately with adequate resolution and then combining the results, the system achieves high overall measurement precision without requiring expensive wideband high-resolution converters
Solution Approach 2:
The patent applies partial action by focusing high measurement precision requirements only on the narrow subband signals rather than the entire wideband signal. Each subband is processed with sufficient precision for accurate EVM measurement, while the overall system cost is reduced by using multiple lower-cost converters
3Ease of manufacture
If a low-speed digitizer is used to reduce cost, then the bandwidth requirement is reduced, but the ability to test wideband RF signals is limited
Solution Approach 1:
The patent uses a bank of band-pass filters to segment the wideband RF signal into multiple narrow subbands. Each subband can be processed by a low-speed digitizer, and by parallel processing multiple subbands, the system achieves wideband signal analysis capability while using only low-speed, cost-effective digitizers
Solution Approach 2:
The patent transforms the problem from a single-dimension time-domain sampling issue to a multi-dimensional solution involving frequency-domain segmentation. By distributing the bandwidth requirement across multiple frequency channels (subbands) that can be processed in parallel, the system achieves wideband capability without requiring high-speed digitization in the time domain
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
Enables cost-effective and high-accuracy testing of wideband RF signals by reducing the bandwidth requirements for the digitizer, making it feasible to use existing low-speed digitizers for evaluating RF signals in millimeter wave bands.
Implementation Method 1
a variable frequency oscillator that generates a local signal having a variable local frequency fLO1
Implementation Method 2
a first frequency mixer that frequency-mixes a local signal and an RF signal, and generates an intermediate frequency signal having a frequency fC-fLO1
Implementation Method 3
a band-pass type first filter that filters the intermediate frequency signal
Data Source
AI summary
A front-end circuit is used to test an RF signal from an RF device. The RF signal is generated by modulating a carrier signal having a carrier frequency with a wideband baseband signal. A variable frequency oscillator generates a local signal having a variable local frequency. The first frequency mixer frequency mixes a local signal and an RF signal to generate an IF signal having a frequency. A band-pass type first filter filters the IF signal. The local frequency can be selected from a plurality of frequencies having a frequency interval equal to or narrower than a bandwidth of the first filter.