RF Sampling Method Using Half-Frequency Positioning

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Solution Overview

Problem

Current radiofrequency reception systems face challenges in reducing manufacturing costs and increasing integration density due to complex low-pass filter production and noise issues associated with CMOS technology, particularly in low-IF and zero-IF architectures.

Innovation Solution

A new sampling method for analog radiofrequency signals that filters frequencies to bring the useful signal to half of the sampling frequency, using a sampling frequency ratio of Ndiv1+½, and incorporates anti-alias filtering with cardinal sine type filters to eliminate parasite frequencies, allowing for integration in CMOS technology while minimizing noise and image frequency issues.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If low-IF or zero-IF architectures are used to reduce manufacturing costs, then integration density is improved, but noise at 1/f increases and image frequency elimination becomes difficult

Engineering Contradiction:

Improvemanufacturing costVSAvoidnoise at 1/f

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The patent changes the sampling frequency parameter to a specific relationship with the carrier frequency (Fs = 2*Fc/(N+1) where N is an integer), which transforms the frequency spectrum such that the useful signal is positioned at half the sampling frequency. This parameter change allows the system to operate in a frequency region where 1/f noise is minimized while maintaining effective image frequency rejection through the resulting spectral arrangement.

Inventive Principle:

Principle #35Parameter changes

2Device complexity

If low-pass filters are used for signal processing in low-IF architecture, then manufacturing complexity is reduced, but filter production becomes difficult and signal attenuation increases

Engineering Contradiction:

Improvefilter production complexityVSAvoidfilter performance

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

Instead of using traditional low-pass filters that attenuate high frequencies, the patent inverts the approach by using high-pass filter characteristics through the sampling process itself. By positioning the useful signal at half the sampling frequency and using the spectral folding properties of sampling, the system naturally rejects low-frequency components and image frequencies without requiring complex low-pass filter structures, thereby simplifying manufacturing while maintaining precision.

Inventive Principle:

Principle #13The other way round (Inversion)

3Measurement precision

If sampling frequency is increased to reduce aliasing, then signal accuracy is improved, but device complexity and cost increase

Engineering Contradiction:

Improvesignal accuracyVSAvoidsystem complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent employs a specific parameter relationship between sampling frequency and carrier frequency (Fs = 2*Fc/(N+1)) that optimizes the balance between accuracy and complexity. This parameter choice positions the useful signal at half the sampling frequency, which provides sufficient spectral separation to prevent aliasing of image frequencies while maintaining a manageable sampling rate that can be implemented with standard CMOS technology, thus avoiding excessive system complexity.

Inventive Principle:

Principle #35Parameter changes

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

This approach reduces signal attenuation, eliminates noise at 1/f, and optimizes integration density by using passive filters, enabling efficient radiofrequency reception systems that can handle stricter standards like GSM and UMTS without significant signal modification or increased costs.

Implementation Method 1

a mixer (4, 5) for converting the frequency to a low intermediate frequency. To achieve this, the mixer (4) receives a frequency corresponding to the sum of the intermediate frequency and the signal carrier frequency on its second input connected to a local oscillator (6)

Methodology Applied

Scientific EffectFrequency translation: Heterodyne

Implementation Method 2

Each mixer (4, 5) is followed by a low pass filter (LPF) (7, 8) respectively to eliminate channels adjacent to the channel that is to be received and parasite frequencies due to aliasing. When a signal being sampled at a sampling frequency Fech includes frequency components with a frequency of more than Fech/2, these frequency components are folded

Methodology Applied

Scientific EffectFrequency selective filtering: Filter (electronic)

Data Source

PatentUS7634247B2Method of sampling an analogue radiofrequency signal

Publication Date: 2009.12.15 STMICROELECTRONICS FRANCE

AI summary

A method for sampling an analogue radiofrequency signal comprising reception of the analogue radiofrequency signal, sending of the received signal on two analogue channels, each channel performing a first signal sampling operation, including a filtering step eliminating signal frequencies that could fold on the useful signal during sampling such that the sampled signal represents a filtered version of the received signal, wherein the sampling frequency is taken to be equal to the frequency of the signal carrier divided by a factor Ndiv1+½, Ndiv1 being an integer number, to bring the useful signal to half of the sampling frequency after sampling.