Extended Impedance-Matching LNA Load Circuits for OOB Rejection
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Solution Overview
Problem
Conventional LNA architectures struggle to achieve wideband output impedance matching, high gain, and high-frequency out-of-band (OOB) rejection, particularly in 5G mobile network bands and millimeter wave ranges, leading to degraded receiver performance due to tradeoffs in gain, bandwidth, and linearity.
Innovation Solution
The proposed LNA circuits incorporate a load circuit with multiple LC resonators and tunable components, including adjustable capacitors and inductors, to achieve wideband output impedance matching, high gain, and OOB harmonic frequency rejection, allowing for programmable operation modes to optimize gain versus linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a single-stage LC output impedance matching circuit is used, then high gain is achieved, but output impedance matching bandwidth is narrow
Solution Approach 1:
The output impedance matching circuit is divided into two independent stages: a first LC matching stage connected to the amplifier core and a second LC matching stage connected to the output terminal. Each stage can be independently optimized for different frequency ranges, allowing the first stage to provide high gain at lower frequencies while the second stage extends the matching bandwidth to higher frequencies, thereby resolving the contradiction between gain and bandwidth.
2Device complexity
If traditional LNA architecture is used, then circuit simplicity is maintained, but high-frequency OOB rejection is insufficient
Solution Approach 1:
A second LC matching stage is introduced as an intermediary between the first LC matching stage and the output terminal. This intermediate stage functions as a band-pass filter that selectively passes the desired frequency band while attenuating out-of-band harmonic frequencies. The addition of this intermediary component improves OOB rejection while maintaining reasonable circuit complexity through the use of standard LC tank circuits.
3Adaptability or versatility
If LC matching components are optimized for wide bandwidth, then output impedance matching bandwidth is improved, but gain is reduced
Solution Approach 1:
The bandwidth requirement is segmented across two LC matching stages with different design optimizations. The first LC stage is optimized for high gain with moderate bandwidth, while the second LC stage is optimized for extended bandwidth with appropriate gain contribution. This segmentation allows each stage to operate at its optimal performance point, achieving overall wide bandwidth without sacrificing the high gain capability of the first stage.
Solution Approach 2:
The two LC matching stages are combined in series between the amplifier core and the output terminal. The composite matching network leverages the complementary strengths of each stage: the first stage provides high gain and the second stage provides bandwidth extension. The combined effect achieves both wide output impedance matching bandwidth and high gain, resolving the tradeoff between these two parameters.
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
The solution enables improved linearity and sensitivity of RF front-end receiver chains by suppressing higher-order OOB harmonics, maintaining in-band high gain and wideband output impedance matching, and supporting multiple operation modes for enhanced performance.
Implementation Method 1
The load circuit includes a first LC resonator coupled between the radio frequency amplifier core and a node, the first LC resonator including a first inductor and a first capacitor coupled in parallel; a second LC resonator coupled between the node and the output terminal
Data Source
AI summary
Circuits and methods for an amplifier (particularly LNAs) that achieve wideband output impedance matching and high gain while simultaneously rejecting out-of-band (OOB) harmonic frequencies. Some embodiments allow multiple modes of operation to allow selection of gain versus linearity characteristics. One aspect of the present invention is improvement of the linearity and sensitivity of a whole RF “front end” (RFFE) receiver chain by suppressing OOB gain within an LNA component at higher order harmonic frequencies. Another aspect of the present invention are new wideband and ultra-wideband LNA load circuits that, while achieving high frequency OOB rejection, maintain in-band high gain and wideband output impedance matching at the same time. Yet another aspect of the present invention are new ultra-wideband LNA output impedance matching circuits.