Low-IF Receiver Controller for IQ Imbalance Interference

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Solution Overview

Problem

Low intermediate frequency (low-IF) receivers face challenges in maintaining operational and performance stability due to space constraints and interference from image signals generated by IQ imbalances, which affect signal-to-noise ratio and system performance.

Innovation Solution

A receiver design that includes a controller to set the first and second local oscillators such that complex IQ signals and interfering signals have the same sign and non-overlapping bands at the input of the complex mixer, utilizing an interference detector and SNR estimator to correct for IQ imbalances and filter out unwanted images.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If local oscillators are set to downconvert desired channels, then channel reception is enabled, but image frequencies and interfering signals are generated that degrade signal-to-noise ratio

Engineering Contradiction:

Improveoperational stabilityVSAvoidinterfering signals

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent converts the harmful interfering signals generated by IQ imbalance into a solvable problem by detecting them and using them to adjust local oscillator settings. The interference detector identifies interfering signals, and the controller uses this information to reposition local oscillators so that interfering signals fall into filterable frequency ranges, transforming a performance-degrading issue into a controllable parameter.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent implements a feedback loop where the interference detector continuously monitors for interfering signals, and the controller adjusts local oscillator frequencies based on this feedback. This closed-loop system allows the receiver to adaptively optimize its performance by responding to actual interference conditions, improving signal-to-noise ratio while maintaining reliable operation.

Inventive Principle:

Principle #23Feedback

2Ease of operation

If device size is reduced to improve portability, then ease of carrying is enhanced, but space for communications circuitry is limited affecting performance stability

Engineering Contradiction:

ImproveportabilityVSAvoidperformance stability

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The patent employs dynamic adjustment of local oscillator frequencies based on detected interfering signals. Rather than using fixed, overly conservative frequency settings that would require larger spacing between components, the system dynamically adapts its operating parameters to actual interference conditions, allowing compact design while maintaining performance stability through real-time optimization.

Inventive Principle:

Principle #15Dynamics

3Productivity

If IQ imbalance is present in complex IQ signals, then signal processing can be performed, but interfering signals are generated that overlap with desired signals

Engineering Contradiction:

Improvesignal processing capabilityVSAvoidinterfering images

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent introduces an intermediary approach by using the interference detector as a mediator between the signal processing chain and the local oscillator control. This intermediary component identifies interfering signals and enables coordinated adjustment of local oscillators, allowing the system to maintain IQ signal processing capability while eliminating the harmful overlapping images through frequency repositioning.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 design enhances the signal-to-noise ratio and system performance by ensuring that interfering images are filtered out, improving the overall stability and efficiency of the low-IF receiver.

Implementation Method 1

a first local oscillator (LO), with a pair of IQ mixers coupled to the first LO and configured to generate complex IQ signals

Methodology Applied

Scientific EffectMixing:

Implementation Method 2

a controller may be coupled between the pair of IQ mixers and the complex mixer and may be configured to set the first LO and the second LO so that the complex IQ signals and an interfering signal generated due to the IQ imbalance

Methodology Applied

Scientific EffectFrequency tuning:

Data Source

PatentEP2568614B1Receiver having controller to set local oscillators so as to render interfering signals filterable and associated methods

Publication Date: 2015.08.26 BLACKBERRY LTD

Figure 1
Figure 2
Figure 3A~3B

AI summary

A receiver 10 includes a first local oscillator (LO) 17, with a pair of in-phase and quadrature (IQ) mixers 16a, 16b coupled to the first LO and configured to generate complex IQ signals having an IQ imbalance. The receiver also includes a second LO 32, with a complex mixer 22 coupled to the second LO and configured to mix the complex IQ signals and generate intermediate frequency (IF) signals based thereon. A controller 30 is coupled between the pair of IQ mixers and the complex mixer and configured to set the first LO and the second LO so that the complex IQ signals and an interfering signal generated due to the IQ imbalance of the complex IQ signals have a same sign and non-overlapping bands at an input of the complex mixer.