Transmitter Noise Suppression via Feedback Loop

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Solution Overview

Problem

Full duplex transceivers face challenges in suppressing noise leakage from the transmitter path to the receiver path, particularly for short duplex distances, due to the limitations of SAW filters in terms of cost, space, and power consumption, and the instability caused by high-order low-pass filters in feedback systems.

Innovation Solution

A feedback loop is implemented around the amplifier in the RF signal processing stage, tapping the RF signal downstream, down-converting it to baseband frequency, removing the baseband signal component, and up-converting the noise component back to RF frequency to suppress noise, while using low-pass filters that are not too sharp to avoid stability issues.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If a SAW filter is placed in the TX path between the VGA and the PA to reduce noise leakage, then noise leakage from TX path to RX path is reduced, but cost and space requirements increase

Engineering Contradiction:

Improvenoise leakageVSAvoidcost and space

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent extracts the noise suppression function from the traditional SAW filter approach and implements it through a feedback loop that processes only the noise component. The feedback loop taps the RF signal downstream of the amplifier, down-converts it to baseband, removes the baseband signal component, and feeds back only the noise component for suppression, thereby eliminating the need for expensive SAW filters while maintaining noise reduction effectiveness.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent introduces a feedback loop coupled around the amplifier in the RF signal processing stage. The feedback loop taps the RF signal downstream of the amplifier, down-converts it to baseband frequency, removes the baseband signal component, and feeds back the noise component to suppress noise leakage. This feedback mechanism enables effective noise suppression without requiring external SAW filters, thereby reducing cost and space requirements.

Inventive Principle:

Principle #23Feedback

2Object-affected harmful factors

If power consumption in the TX path is increased to reduce noise generated in the TX path, then noise generated in TX path is reduced, but power consumption increases

Engineering Contradiction:

Improvenoise generatedVSAvoidpower consumption

Core Design Contradiction:

Object-affected harmful factorsVSUse of energy by moving object

Solution Approach 1:

Inventive Principle:

Principle #23Feedback

3Object-affected harmful factors

If high-order low-pass filters are used in the feedback loop to suppress noise, then noise suppression is improved, but stability of the feedback system deteriorates

Engineering Contradiction:

Improvenoise suppressionVSAvoidfeedback system stability

Core Design Contradiction:

Object-affected harmful factorsVSStability of the object's composition

Solution Approach 1:

The patent changes the parameter of filter sharpness by using low-pass filters that are not too sharp. This modification in the filter characteristic allows the feedback system to maintain stability while still achieving effective noise suppression. The feedback loop taps the RF signal downstream of the amplifier, down-converts it to baseband frequency, removes the baseband signal component, and feeds back the noise component with appropriate filtering that balances noise reduction and system stability.

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 effectively reduces noise leakage and improves the linearity of the transmitter device, reducing power consumption and eliminating the need for external filters, thereby enhancing the Adjacent Channel Leakage Ratio (ACLR) and Signal-to-Noise Ratio (SNR) without causing stability problems.

Implementation Method 1

a modulator for converting a baseband signal into an RF signal

Methodology Applied

Scientific EffectModulation:

Implementation Method 2

an amplifier, and a feedback loop coupled around the amplifier

Methodology Applied

Scientific EffectAmplification:

Implementation Method 3

a feedback loop coupled around the amplifier

Methodology Applied

Scientific EffectFeedback: Feedback

Data Source

PatentUS8755758B2Technique for suppressing noise in a transmitter device

Publication Date: 2014.06.17 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

AI summary

A technique of suppressing noise in a transmitter device (300) is provided, wherein the transmitter device (300) comprises a baseband signal processing stage (301) operating at baseband frequency and comprising a modulator (316, 320) for converting a baseband signal into an RF signal, and an RF signal processing stage (301) operating at RF and comprising an amplifier (330). A method implementation of this technique comprises the steps performed in a feedback loop (333, 336) coupled around the amplifier (330) of tapping the RF signal processing stage downstream of the amplifier (330) to obtain an amplified RF signal comprising a baseband signal component and a noise component, downconverting the tapped RF signal to baseband frequency, removing the baseband signal component from the downconverted signal, upconverting the resulting signals still comprising the noise component to RF frequency and feeding the upconverted signal back to the RF signal processing stage upstream of the amplifier (330) thereby suppressing the noise component.