RF Downconversion Mixer With Common-Mode Feedback for IM2 Suppression

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Mixer designs, such as Gilbert-type mixers, suffer from second-order intermodulation distortion (IM2) due to self-mixing and duty-cycle errors, causing unwanted low-frequency components to leak into the differential mode output, which complicates subsequent signal processing.

Innovation Solution

A mixer with a common mode feedback loop that detects deviations in the common mode output and modifies the drain current of RF transistors to reduce second-order distortion, using a common mode sensing component and feedback path to subtract deviations from the drain current, potentially amplifying the correction before subtraction.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If a differential output mixer is used to remove IM2 as common-mode signal, then second-order distortion is reduced, but duty-cycle errors cause IM2 to leak into differential mode

Engineering Contradiction:

Improvesecond-order distortionVSAvoidcommon-mode rejection

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The patent implements a feedback mechanism that senses the common-mode output voltage and uses it to generate a correction signal. This feedback loop detects deviations from ideal common-mode behavior and actively compensates for duty-cycle errors, preventing IM2 leakage into the differential output while maintaining the benefits of differential architecture

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent introduces an intermediary sensing circuit that measures the common-mode voltage and translates it into a corrective action. This intermediary component bridges the gap between the differential mixer core and the common-mode rejection requirement, allowing the system to maintain both differential output benefits and common-mode suppression

Inventive Principle:

Principle #24Intermediary (Mediator)

2Object-affected harmful factors

If common mode feedback loop is added to reduce IM2 leakage, then second-order distortion is reduced, but device complexity increases

Engineering Contradiction:

ImproveIM2 leakageVSAvoidfeedback circuit complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent designs the common-mode sensing and feedback circuit to serve multiple functions: it senses common-mode voltage, generates correction signals, and compensates for duty-cycle errors simultaneously. This multi-functionality reduces the need for separate circuits, thereby limiting the increase in overall device complexity while achieving IM2 leakage reduction

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS8131245B2Mixer for downconversion of RF signals

Publication Date: 2012.03.06 QUALCOMM TECH INT

AI summary

A mixer for downconversion of RF signals includes at least one RF transistor (305); at least one switching pair (303) connected to the drain current (301) of the at least one RF transistor (305); and a common mode sensing component (300) configured to detect deviations in the common mode output of the switching pair (303) from a specified output; wherein the deviations modify the current of the at least one switching pair (303).