Adaptive RF Receiver Filter for DC Distortion Mitigation

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Solution Overview

Problem

Direct Conversion Receivers (DCR) and Very Low Intermediate Frequency (VLIF) receivers face challenges with noise and distortion introduction during down conversion, particularly from strong digital mobile radio interferers, which degrade blocking performance and require improved interference detection and mitigation.

Innovation Solution

The method involves receiving an RF signal, down-converting it to an intermediate frequency, detecting off-channel interference and direct current (DC) shifts, determining filter settings based on detected interference, and using adaptive filters to mitigate DC distortion, enabling faster and more reliable detection and removal of interferers.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If DCR or VLIF receivers are used for low cost and small size operation, then receiver cost and size are reduced, but blocking performance degrades due to chopper noise from strong interferers

Engineering Contradiction:

Improvereceiver cost and sizeVSAvoidblocking performance degradation from chopper noise

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The patent applies preliminary action by detecting interferers before they cause significant chopper noise degradation and proactively adjusting filter settings. The system continuously monitors the RF signal for interferer presence and pre-adjusts the IF filter bandwidth and notch filter parameters to prevent blocking performance degradation before it occurs.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements feedback by continuously monitoring the down-converted signal for DC transitions and chopper noise indicators, then using this information to dynamically adjust IF filter settings. The system measures the actual signal conditions and feeds this information back to the filter control logic to optimize filtering parameters in real-time, thereby maintaining blocking performance while operating in cost-effective DCR or VLIF architectures.

Inventive Principle:

Principle #23Feedback

2Object-affected harmful factors

If adaptive filtering is applied to mitigate DC distortion, then interference mitigation improves, but device complexity increases

Engineering Contradiction:

ImproveDC distortion and interferer mitigationVSAvoidfilter control mechanism complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent applies parameter changes by dynamically adjusting IF filter bandwidth and notch filter parameters based on detected interferer characteristics. When strong interferers are detected, the system modifies filter Q-factor, bandwidth, and center frequency parameters to optimize rejection of specific interferers while maintaining passband signal integrity. This adaptive parameter adjustment provides effective DC distortion mitigation without requiring complex architectural changes.

Inventive Principle:

Principle #35Parameter changes

3Measurement precision

If interferer detection sensitivity is increased to detect low-power interferers, then detection capability improves, but false detection rate increases

Engineering Contradiction:

Improveinterferer detection sensitivityVSAvoidfalse detection rate

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent uses an intermediary approach by introducing a dedicated interferer detection module that monitors the RF signal path before down-conversion. This separate detection path uses different signal processing techniques to identify interferers without being affected by the same noise and distortion mechanisms that affect the main receive path, thereby improving detection sensitivity while maintaining reliability through spatial separation of detection and reception functions.

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 approach enhances the detection of low-power interferers and effectively removes or mitigates DC distortion, improving the receiver's ability to handle interference and maintain performance.

Implementation Method 1

These receivers combine a received radio frequency (RF) signal with a local oscillator signal prior to analogue to digital conversion

Methodology Applied

Scientific EffectMixing: Heterodyne

Implementation Method 2

Often during down conversion, noise, distortion or imbalance is introduced into, or pronounced in, the I and Q components

Methodology Applied

Scientific EffectFiltering: Filter (electronic)

Data Source

PatentUS9800277B2Interference detection and mitigation in radio frequency receivers

Publication Date: 2017.10.24 MOTOROLA SOLUTIONS INC

AI summary

A radio frequency (RF) receiver and method of controlling an RF receiver are provided. The method includes receiving an RF signal and down-converting the RF signal to a substantially baseband signal. A direct current (DC) transition is detected in a portion of the substantially baseband signal. The substantially baseband signal is then filtered using a first filter configuration at the portion of the substantially baseband signal including the DC transition and a second filter configuration at a portion of the substantially baseband signal not including the DC transition.