Transformer-Feedback Low Noise Amplifier for Wideband Input Matching
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Solution Overview
Problem
Designing a low noise amplifier for RF receivers is challenging due to conflicting requirements such as high linearity, large conversion gain, low noise figure, and wide input match bandwidth, especially when handling strong interference levels like those encountered in GSM signals, where existing common source and common gate structures fail to suppress out-band interference effectively.
Innovation Solution
A low noise amplifier configuration using a common source amplifying transistor with a self-coupled step-up transformer and feedback path, along with a source follower and tuneable capacitors, which maintains low voltage gain for linearity while boosting feedback voltage gain for input matching, and includes a balun circuit to convert single-ended signals to differential signals, allowing for improved noise figure and bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If common source or common gate low noise amplifier structures are used, then the amplifier can provide gain, but the interference signal swing is too high causing nonlinearities at input, interconnection, or output nodes
Solution Approach 1:
The patent divides the amplifier into two distinct stages: a common gate stage for input matching and a common source stage for high gain. This segmentation allows each stage to be optimized for its specific function, with the common gate stage handling impedance matching and the common source stage providing voltage gain, thereby maintaining linearity while achieving high gain overall.
Solution Approach 2:
The patent introduces a buffer stage between the common gate and common source stages. This buffer acts as an intermediary that isolates the high-impedance output of the common gate stage from the low-impedance input of the common source stage, preventing nonlinearities at the interconnection node while allowing both stages to operate optimally.
2Manufacturing precision
If feedback path is added to improve input matching, then input matching bandwidth is improved, but voltage gain at output node must be higher or feedback resistance must be small leading to large noise contribution
Solution Approach 1:
The patent implements a feedback path from the output of the common source stage back to the input of the common gate stage. This feedback improves input matching and extends bandwidth without requiring high voltage gain at the output node or small feedback resistance, thereby avoiding the noise figure penalty that would otherwise result.
3Reliability
If voltage gain of low noise amplifier is increased to use larger feedback resistance, then noise contribution from feedback resistance is reduced, but output voltage swing must be low to meet linearity requirement
Solution Approach 1:
The two-stage architecture allows the common gate stage to provide the necessary voltage gain early in the signal path, enabling the use of larger feedback resistance in the feedback path without requiring additional gain later. This segmentation of gain provision allows larger feedback resistance (reducing noise) while keeping the final output voltage swing within linear limits.
4Manufacturing precision
If common gate low noise amplifier is used for wide band input matching, then input matching bandwidth is improved, but power gain is not enough and noise figure is high
Solution Approach 1:
The patent uses a common gate stage for input matching (providing wide bandwidth) followed by a common source stage for high voltage gain. This segmentation allows the system to achieve both wide input matching bandwidth and high power gain, overcoming the limitations of using either stage alone.
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 achieves high linearity, wide input match bandwidth, and decent noise figure without increasing power consumption, effectively suppressing out-band interference and providing adequate conversion gain, even under strong RF interference conditions.
Implementation Method 1
a self-coupled step-up transformer having at least one primary winding connected to a supply voltage and the drain terminal of the at least one amplifying transistor and at least one self-coupled secondary inductor winding arranged in said feedback path
Implementation Method 2
includes a balun circuit to convert single-ended signals to differential signals
Data Source
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AI summary
A low noise amplifier comprises at least one amplifying transistor (Ts1; Ts2) configured in a common source configuration to receive an input signal (RFin) at a gate terminal and provide an amplified signal at a drain terminal and at least one feedback path arranged to couple a part of the amplified signal back to the gate terminal and comprising a feedback impedance. The low noise amplifier further comprises a self-coupled step-up transformer having at least one primary winding (Lp) connected to a supply voltage (Vdd) and the drain terminal of the at least one amplifying transistor and at least one self-coupled secondary inductor winding (Lf1; Lf2) arranged in the feedback path. The low noise amplifier provides a better suppression for out-band interference and at the same time it has a wider input match bandwidth, decent conversion gain and decent noise figure without increasing power consumption.