LNA Post-Distortion Cancellation Using Phase-Shifted Diode IM3

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Solution Overview

Problem

Common source low noise amplifiers (LNAs) face challenges in linearity due to nonlinearity of current, which affects noise figure and gain performance, especially under stringent carrier aggregation mode receiver sensitivity requirements.

Innovation Solution

Incorporating a post distortion cancellation block with a diode coupled in series with phase-shift logic, which generates an opposite signed third-order intermodulation magnitude to cancel nonlinear currents without degrading the noise figure, using resistor-capacitor circuits with variable components for optimal phase and bias settings.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a common source LNA topology is used to achieve low noise figure performance, then noise figure is improved, but linearity deteriorates due to nonlinearity of current

Engineering Contradiction:

Improvenoise figureVSAvoidlinearity

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The LNA is divided into two separate paths: a main path that provides high gain and low noise figure, and a cancellation path that specifically targets and removes nonlinear distortion products. This segmentation allows each path to be optimized for its specific function without compromising the other.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The nonlinear distortion products generated by the main LNA path are not simply suppressed but are actively captured, phase-shifted, and inverted in the cancellation path. By converting the harmful distortion into a useful cancellation signal, the system transforms the problem of nonlinearity into a solution that actively removes distortion while preserving the low noise figure performance of the common source topology.

Inventive Principle:

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

2Object-generated harmful factors

If distortion cancellation techniques are applied to improve linearity, then linearity is improved, but noise figure degrades

Engineering Contradiction:

ImprovelinearityVSAvoidnoise figure

Core Design Contradiction:

Object-generated harmful factorsVSReliability

Solution Approach 1:

The cancellation path is segmented into distinct functional blocks: a distortion extraction stage that captures nonlinear products, a phase-shift network that adjusts the phase of these products, and a combination stage that merges the canceled signal with the main path output. This segmentation ensures that noise added during cancellation is minimized and does not significantly impact the overall noise figure.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The system dynamically adjusts parameters such as phase shift amount and cancellation signal amplitude based on operating conditions. By optimizing these parameters, the system achieves effective distortion cancellation while minimizing the impact on noise figure, maintaining NF degradation of less than 0.03 dB across various operating points.

Inventive Principle:

Principle #35Parameter changes

3Adaptability or versatility

If discrete external components are used for front-end circuit blocks to perform filtering and switching functions, then functionality is improved, but device size and cost increase

Engineering Contradiction:

ImprovefunctionalityVSAvoiddevice size

Core Design Contradiction:

Adaptability or versatilityVSArea of stationary object

Solution Approach 1:

Multiple front-end functions including filtering, switching, impedance matching, and distortion cancellation are merged into a single integrated circuit. The distortion cancellation block incorporates diodes, phase-shift logic, and biasing circuits that work together in an integrated manner, eliminating the need for separate discrete components and reducing overall device size and cost.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The distortion cancellation block is designed with multi-functionality, serving both as a linearization element and as part of the overall signal processing chain. The same circuit structures perform multiple roles: the diodes provide both distortion generation and phase shifting, while the biasing network simultaneously controls multiple operating points. This multi-functionality reduces the total component count and integrated circuit area.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 configuration improves linearity within the common source LNA topology by effectively canceling nonlinearities while maintaining a low noise figure, achieving less than 0.03 dB NF degradation compared to previous solutions that degrade by more than 0.3 dB.

Implementation Method 1

generates an opposite signed third-order intermodulation magnitude to cancel nonlinear currents

Methodology Applied

Scientific EffectIntermodulation:

Implementation Method 2

phase-shift logic may be coupled in series with the diode

Methodology Applied

Scientific EffectPhase shift:

Data Source

PatentUS10566937B2Post distortion cancellation with phase shifter diode for low noise amplifier

Publication Date: 2020.02.18 QUALCOMM INC

AI summary

A low noise amplifier may include a post distortion cancellation block coupled to the low noise amplifier. The post distortion cancellation block may include a diode, and phase-shift logic. The phase-shift logic may be coupled in series with the diode.