Harmonic Rejection Mixer Using Phase-Offset LO Division

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Solution Overview

Problem

Conventional RF transmitters generate undesirable noise due to odd harmonics, which can violate transmit mask requirements and cause distortions, requiring high-Q filters that are bulky, power-consuming, and narrow-band.

Innovation Solution

A harmonic rejection mixer system using a local oscillator, a divide-by-N frequency divider, a divide-by-three frequency divider, and a harmonic rejection mixer to eliminate third frequency harmonics, replacing poly-phase filters with a compact, low-power, wide-band implementation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-generated harmful factors

If a conventional mixer is used to upconvert baseband signals, then the upconversion function is achieved, but odd harmonics are generated causing unwanted noise and spurious power

Engineering Contradiction:

Improveodd harmonicsVSAvoidtransmit mask requirements

Core Design Contradiction:

Object-generated harmful factorsVSReliability

Solution Approach 1:

The LO signal is segmented into multiple phase-offset signals (0°, 60°, 120°) using frequency dividers. These segmented signals are then processed through separate mixer paths and combined to cancel harmonics while preserving the fundamental frequency

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention converts the harmful odd harmonics into a beneficial cancellation mechanism. By using three phase-offset LO signals and appropriate weighting in the mixer outputs, the third harmonics from each path cancel each other out, while the fundamental frequencies constructively interfere to produce the desired output

Inventive Principle:

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

2Object-generated harmful factors

If a high-Q filter is used to reject odd harmonics, then harmonic rejection is improved, but the device becomes bulky and power-consuming

Engineering Contradiction:

Improveharmonic rejectionVSAvoidfilter requirements

Core Design Contradiction:

Object-generated harmful factorsVSDevice complexity

Solution Approach 1:

The harmful harmonic rejection function is extracted from the traditional high-Q filter and implemented through the harmonic rejection mixer architecture. The mixer uses phase-offset LO signals and specific combining weights to inherently reject third harmonics without requiring external filtering components

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The mechanical/high-Q filter system is replaced with an electronic signal processing system. Instead of using physical filtering components that require high quality factors, the invention uses electronic phase manipulation and signal combining to achieve harmonic rejection

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Ease of operation

If poly-phase filters are used to generate phase-offset signals, then the required phase signals are produced, but the system becomes bulky and narrow-band

Engineering Contradiction:

Improvephase signal generationVSAvoidbandwidth

Core Design Contradiction:

Ease of operationVSAdaptability or versatility

Solution Approach 1:

The poly-phase filter system is replaced with digital frequency divider circuits. These dividers generate the required 0°, 60°, and 120° phase-offset signals through digital counting and selection, eliminating the need for bulky analog filter networks and enabling wideband operation

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

4Ease of operation

If poly-phase filters are used to generate phase-offset signals, then the required phase signals are produced, but power consumption increases

Engineering Contradiction:

Improvephase signal generationVSAvoidpower consumption

Core Design Contradiction:

Ease of operationVSUse of energy by stationary object

Solution Approach 1:

The power-consuming poly-phase filter system is replaced with efficient digital frequency divider circuits. These dividers use minimal power to generate the required phase-offset signals by utilizing digital logic rather than power-hungry analog filter components

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS8165538B2Systems and methods for implementing a harmonic rejection mixer

Publication Date: 2012.04.24 SKYWORKS SOLUTIONS INC

AI summary

Various embodiments of systems and methods for generating local oscillator (LO) signals for a harmonic rejection mixer are provided. One embodiment is a system for generating local oscillator (LO) signals for a harmonic rejection mixer. One such system comprises a local oscillator, a divide-by-N frequency divider, a divide-by-three frequency divider, and a harmonic rejection mixer. The local oscillator is configured to provide a reference frequency signal. The divide-by-N frequency divider is configured to divide the reference frequency signal by a value N and provide an output signal. The divide-by-three frequency divider is configured to receive the output signal of the divide-by-N frequency divider and divide the output signal into three phase-offset signals. The harmonic rejection mixer is configured to receive the three phase-offset signals and eliminate third frequency harmonics.