Multiple Mixer Input Network With Floating Line Feedthrough Rejection

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Solution Overview

Problem

Designing satisfactory mixers and local oscillator circuitry for electronic devices with wireless communications capabilities is challenging due to issues with undesired oscillator feedthrough and spurious emissions in modern transceiver designs.

Innovation Solution

Implementing impedance matching circuits with capacitive filters and floating transmission lines to mitigate oscillator feedthrough by rejecting harmonic signals and spurious emissions in mixers sharing a common input matching network.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If multiple mixers share a common input matching network, then device complexity is reduced, but oscillator feedthrough and spurious emissions increase

Engineering Contradiction:

Improvecomplexity of mixer and matching network configurationVSAvoidoscillator feedthrough and spurious emissions

Core Design Contradiction:

Device complexityVSObject-generated harmful factors

Solution Approach 1:

A floating transmission line resonator is introduced as an intermediary element between the common input matching network and the mixer inputs. This resonator acts as a mediator that selectively rejects oscillator feedthrough and spurious emissions at specific harmonic frequencies while allowing desired signal frequencies to pass through, thus resolving the contradiction between shared matching network complexity and harmful emissions

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The floating transmission line resonator utilizes parameter changes in its electrical characteristics at different frequencies. By designing the resonator with specific length and impedance parameters, it creates frequency-selective rejection characteristics that block harmonic frequencies (where feedthrough occurs) while maintaining proper matching at operating frequencies, thereby reducing harmful emissions without increasing overall system complexity

Inventive Principle:

Principle #35Parameter changes

2Object-generated harmful factors

If oscillator feedthrough is mitigated using traditional filtering methods, then spectral emissions are reduced, but mixer performance and signal-to-noise ratio deteriorate

Engineering Contradiction:

Improvespectral emissionsVSAvoidmixer performance and signal-to-noise ratio

Core Design Contradiction:

Object-generated harmful factorsVSReliability

Solution Approach 1:

The floating transmission line resonator provides localized frequency-selective filtering at specific points in the circuit (between the matching network and mixer inputs). Instead of applying broad filtering that would affect all frequencies, the resonator is designed to have specific rejection characteristics only at harmonic frequencies where feedthrough occurs, leaving the desired signal frequencies unaffected and maintaining mixer performance

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The floating transmission line resonator operates on principles analogous to mechanical resonance, where it is designed to resonate at specific harmonic frequencies to create high impedance paths that block feedthrough signals. This resonant behavior allows selective rejection of unwanted frequencies while maintaining low impedance paths for desired frequencies, thus reducing spectral emissions without degrading signal-to-noise ratio

Inventive Principle:

Principle #18Mechanical vibration

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

Reduces undesired oscillator feedthrough and suppresses spectral emissions, enhancing the performance of wireless communications circuitry in electronic devices.

Implementation Method 1

a floating transmission line interposed between the first and second transmission lines and configured to reject signals with a frequency equal to a multiple of the oscillation frequency

Methodology Applied

Scientific EffectResonance: Resonance

Implementation Method 2

one or more harmonic rejection capacitors coupled to the input of the first mixer and configured to reject harmonic signals, at the input of the first mixer, with a harmonic frequency equal to an integer multiple of the oscillation frequency

Methodology Applied

Scientific EffectCapacitive filtering: Capacitance

Implementation Method 3

one or more filter capacitors coupled to a node between the first mixer and the first transmission line path and configured to filter spurious signals, associated with the oscillating signal, at the node

Methodology Applied

Scientific EffectCapacitive filtering: Capacitance

Data Source

PatentUS20260051850A1Oscillator Feedthrough Mitigation for Multiple Mixers

Publication Date: 2026.02.19 APPLE INC

AI summary

Circuitry is provided that includes a matching circuit, a first mixer coupled to the matching circuit and configured to receive a signal with an oscillation frequency, a second mixer coupled to the matching circuit, a first transmission line path coupled between the matching circuit and an input of the first mixer, and one or more capacitors coupled to the input of the first mixer and configured to reject signals at a harmonic frequency of the oscillation frequency. The wireless circuitry can further include a second transmission line path coupled between the matching circuit and an input of the second mixer. The transmission line path can include a first transmission line for conveying signals between the matching circuit and the first mixer, a second transmission line for conveying signals between the matching circuit and the first mixer, and a floating transmission line interposed between the first and second transmission lines.