Dual-Path LNA Harmonic Cancellation for Better Linearity
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Solution Overview
Problem
LNA circuits face challenges in achieving ideal linearity due to non-linear transconductance of transistors, leading to noise issues at carrier frequencies from harmonic noise source signals.
Innovation Solution
The implementation of additional transistors MPA and MNA in the LNA circuit, which are biased and sized to cancel out the non-linearity of the transconductance in the first and second signal paths, effectively reducing noise at the carrier frequency by summing harmonic components out-of-phase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If standard transistors are used in the LNA circuit, then the circuit structure remains simple, but the linearity deteriorates due to non-linear transconductance
Solution Approach 1:
The LNA circuit is divided into multiple parallel signal paths (first signal path with transistor MN1, second signal path with transistor MN2). Each path has its own transconductance characteristics, and by segmenting the circuit this way, the patent can combine different transconductance non-linearities to cancel each other out, improving overall linearity without requiring completely new device structures.
Solution Approach 2:
The patent changes the biasing parameters and sizing parameters of the transistors in different signal paths. Specifically, transistors MN1 and MN2 are biased and sized differently so that their transconductance non-linearities have opposite characteristics. By adjusting these parameters, the non-linear terms in the combined output cancel each other, achieving higher linearity while maintaining standard transistor structures.
2Reliability
If additional transistors MPA and MNA are added to cancel non-linearity, then the linearity improves, but the device complexity increases
Solution Approach 1:
Transistors MPA and MNA are merged with the existing signal paths by connecting their drains to the same output node. The additional transistors are combined in parallel with MN1 and MN2 respectively, allowing their transconductance characteristics to interact and cancel non-linearities. This merging approach achieves linearity improvement without requiring completely separate cancellation circuits.
Solution Approach 2:
The patent converts the inherently non-linear transconductance characteristic of MOSFETs, which is normally a harmful effect, into a beneficial property. By carefully designing the biasing and sizing of MPA and MNA, their non-linear transconductance is made to produce cancellation effects that reduce the overall non-linearity of the LNA circuit. The harmful non-linearity is transformed into a linearity-improving mechanism.
Data Source
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AI summary
An amplifier circuit, a receiver circuit thereof and a method of using the amplifier circuit are disclosed. The amplifier circuit includes a first signal path including a first amplifying circuit, where the first amplifying circuit is configured to receive an input signal and to transmit a first amplified output to an output terminal, and where the first amplified output includes first amplifier circuit harmonic noise. The amplifier circuit also includes a second signal path including a second amplifying circuit, where the second amplifying circuit receives an input signal and transmits a second amplified output to the output terminal, and where the second amplified output includes second amplifier circuit harmonic noise. An output signal transmitted by the output terminal includes the first and second amplified outputs, and the first amplifying circuit harmonic noise is at least partially canceled by the second amplifying circuit harmonic noise in the output signal.