LNA Mid-Node Impedance Network for Gain and S11 Trade-Offs

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Solution Overview

Problem

Low noise amplifiers (LNAs) face a trade-off between gain and reflection coefficient, where improving gain can degrade reflection coefficient and vice versa, limiting their suitability for specific applications due to parasitic capacitance effects.

Innovation Solution

Incorporating a mid-node impedance network between the transconductance and cascode devices, which can include resistors, capacitors, and inductors, to compensate for parasitic capacitance and decouple the design trade-off between reflection coefficient and gain, enhancing flexibility in achieving desired S11 and gain/noise figure specifications.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If gain is improved in an LNA, then amplification performance increases, but reflection coefficient degrades

Engineering Contradiction:

ImprovegainVSAvoidreflection coefficient

Core Design Contradiction:

PowerVSReliability

Solution Approach 1:

An impedance matching network is introduced as an intermediary component between the amplifier stage and the output node. This network transforms the output impedance to achieve both high gain and good reflection coefficient simultaneously, resolving the trade-off by mediating the impedance relationship between components.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent employs parameter optimization by adjusting the impedance values and component parameters in the amplifier stage and matching network. By changing these parameters, the design achieves both high gain and acceptable reflection coefficient, moving away from the fixed trade-off relationship.

Inventive Principle:

Principle #35Parameter changes

2Device complexity

If parasitic capacitance is present in the LNA, then device simplicity is maintained, but performance degradation occurs

Engineering Contradiction:

Improveparasitic capacitanceVSAvoidperformance

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent converts the harmful effect of parasitic capacitance into a beneficial design feature by incorporating compensation techniques in the impedance matching network. The network is designed to counteract the parasitic effects, transforming what was previously a performance-degrading factor into an accounted-for parameter that can be optimized.

Inventive Principle:

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

Solution Approach 2:

The impedance matching network serves as an intermediary that isolates the amplifier stage from the effects of parasitic capacitance. By placing this network between the active devices and the output, the parasitic effects are managed without requiring changes to the core amplifier structure.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS11303253B2Apparatus and methods for low noise amplifiers with mid-node impedance networks

Publication Date: 2022.04.12 SKYWORKS SOLUTIONS INC

AI summary

Apparatus and methods for LNAs with mid-node impedance networks are provided herein. In certain configurations, an LNA includes a mid-node impedance circuit including a resistor and a capacitor electrically connected in parallel, a cascode device electrically connected between an output terminal and the mid-node impedance circuit, and a transconductance device electrically connected between the mid-node impedance circuit and ground. The transconductance device amplifies a radio frequency signal received from an input terminal. The LNA further includes a feedback bias circuit electrically connected between the output terminal and the input terminal and operable to control an input bias voltage of the transconductance device.