Inductorless Self-Tuned LNA Input Matching for Low Noise Figure
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Solution Overview
Problem
Low-noise amplifiers (LNAs) face a trade-off between noise figure and input matching, with narrow band LNAs achieving lower noise figures but requiring off-chip matching components, making them less suitable for low-cost applications, while wideband LNAs have higher noise figures. Additionally, LNAs can be nonlinear, leading to earlier saturation and increased noise contribution from subsequent stages.
Innovation Solution
A self-tunable wideband LNA design that eliminates the need for off-chip components by using a common-gate and common-source configuration with a feedback capacitor to reduce noise figure and enhance transconductance, allowing for automatic input resistance matching without inductors, thereby achieving very low noise figures and improved linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If narrow band LNA configuration is used, then noise figure is reduced, but off-chip matching components are required
Solution Approach 1:
The patent extracts and eliminates the off-chip inductor component from the LNA design by implementing an inductorless input matching network using only on-chip capacitors and transistor elements, thereby removing the harmful dependency on external components while maintaining narrowband noise performance
Solution Approach 2:
The patent substitutes the traditional inductor-based input matching network with a capacitor-based resonant circuit combined with transistor impedance transformation, replacing the mechanical/external inductor component with an integrated on-chip electrical solution that achieves the same matching function
2Device complexity
If wideband LNA configuration is used, then integration is improved, but noise figure increases
Solution Approach 1:
The patent implements a dynamically tunable resonant frequency capability through variable capacitor elements and bias control, allowing the LNA to be reconfigured for different frequency bands while maintaining optimal noise performance for each band, thus achieving wideband functionality without permanent noise penalty
Solution Approach 2:
The patent changes the operating parameters by using variable capacitance values and bias conditions to tune the resonant frequency and impedance matching characteristics, enabling the same circuit topology to achieve low noise figure across multiple frequency bands rather than being fixed to a single bandwidth
3Stability of the object's composition
If LNA gain is reduced to prevent saturation, then linearity is improved, but noise contribution of next stages increases
Solution Approach 1:
The patent applies preliminary noise cancellation action by introducing a second transistor that generates an anti-correlated noise signal to cancel the noise from the first transistor before the signal proceeds to subsequent stages, proactively preventing noise accumulation rather than reacting to it later
Solution Approach 2:
The patent converts the harmful noise contribution of the bias and load resistors into a beneficial effect by using the same resistive elements to provide impedance matching and biasing while their noise is cancelled through the correlated noise cancellation mechanism, turning a disadvantage into an advantage
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 a noise figure below 1 dB and reduces the noise contribution of bias and load resistors, enabling cost-effective and compact LNA integration in 4G/5G front-end modules with improved out-of-band linearity and reduced integration costs.
Implementation Method 1
A feedback capacitor is coupled between a gate of the first transistor and the feedback output node
Implementation Method 2
capacitance of the feedback capacitor is sized to eliminate the need for coupling an input impedance matching inductor to the input node and meanwhile reduce the noise figure of the LNA
Data Source
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AI summary
A low-noise amplifier (12) is disclosed having a first transistor (M1) with a first current terminal coupled to a supply voltage rail (VDD) through a load resistor (R1) and a second current terminal coupled to an input node (N1), wherein a bias resistor (Rb1) is coupled between the input node (N1) and a fixed voltage node (GND1). A second transistor (M2) has a third current terminal coupled to an output node (N3) and a fourth current terminal coupled to the fixed voltage node (GND1). A feedback capacitor (C f1 ) is coupled between the input node (N1) and the output node (N3), wherein capacitance of the feedback capacitor (C f1 ) is sized to eliminate the need for coupling an input impedance matching inductor to the input node (N1).