Inductorless Low-Noise Amplifier With Capacitive Feedback Matching
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Solution Overview
Problem
Conventional multiband wireless receivers require multiple expensive and bulky RF preselection filters and low noise amplifiers (LNAs) to handle various frequency bands, which occupy significant silicon area and are prone to interference, especially due to the use of on-chip inductors that pick up digital clock harmonics.
Innovation Solution
A low noise amplifier (LNA) topology using a pair of transconductance amplifiers with a capacitive feedback network, eliminating the need for on-chip inductors and providing impedance matching, thereby reducing noise and increasing linearity while allowing for multiband operation without external filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If on-chip inductors are used in integrated LNAs, then impedance matching and voltage headroom are improved, but silicon area consumption increases significantly and digital interference is picked up
Solution Approach 1:
The patent extracts and removes the on-chip inductor component from the LNA circuit, replacing it with an inductorless topology that uses capacitive feedback and resistive loading to achieve impedance matching without requiring large-area inductive elements
Solution Approach 2:
The patent substitutes the mechanical/physical inductor component with an equivalent electrical circuit implementation using capacitors and resistors in a feedback configuration, replacing the inductive impedance matching mechanism with a capacitive feedback-based matching approach
2Adaptability or versatility
If multiple RF preselection filters and LNAs are used for multiband coverage, then frequency band coverage is improved, but device size and cost increase
Solution Approach 1:
The patent designs a universal inductorless LNA topology that can operate across multiple frequency bands without requiring separate tuned inductors for each band, enabling a single circuit design to serve multiple frequency coverage requirements
Solution Approach 2:
The patent employs dynamic element selection and biasing mechanisms that allow the LNA to adapt its operating characteristics across different frequency bands, enabling multiband operation with a single flexible circuit architecture rather than multiple fixed circuits
3Power
If on-chip inductors are used to tune parasitic capacitances, then LNA gain at frequency of interest is improved, but magnetic coupling interference from digital circuits increases
Solution Approach 1:
The patent removes the inductive elements that are the source of magnetic coupling interference, replacing the inductor-based gain tuning mechanism with a capacitive feedback approach that achieves frequency selectivity without magnetic field generation
Solution Approach 2:
The patent converts the potentially harmful effect of parasitic capacitances into a useful feature by using capacitive feedback to exploit these capacitances for impedance matching and frequency-dependent gain control, turning what was previously a problem into a solution mechanism
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 proposed LNA architecture achieves a low noise figure, high linearity, and reduced silicon area usage, enabling efficient multiband operation with programmable current consumption and lower power consumption, particularly beneficial for battery-powered devices.
Implementation Method 1
the output terminal of the second transconductance amplifier is connected to the input terminal of the second transconductance amplifier via a capacitive feedback network
Data Source
AI summary
A low noise amplifier comprising a first transconductance amplifier arranged to receive an input voltage at its input terminal and to generate an output current at its output terminal. A second transconductance amplifier is arranged such that its input terminal is connected to the input terminal of the first transconductance amplifier, and such that the output terminal of the second transconductance amplifier is connected to the input terminal of the second transconductance amplifier via a capacitive feedback network (C1).