Tunable LNA Feedback Circuit for Wideband Impedance Matching
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Solution Overview
Problem
Designing a low-noise amplifier (LNA) for wideband radio receiver circuits that achieves input impedance matching while maintaining high performance across a large frequency range is challenging, especially when maximum gain and impedance matching occur at different frequencies.
Innovation Solution
Incorporating a tunable tank circuit and a feedback network with a tunable capacitor connected between an internal node of the feedback circuit path and a reference voltage node, allowing for efficient tuning of the amplifier's gain and impedance matching across a wide frequency range using components with low Q value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a tank circuit is used to provide frequency selectivity, then frequency selectivity is improved, but the phase changes abruptly around resonance frequency making input impedance matching difficult
Solution Approach 1:
The patent applies feedback by connecting a feedback network between the output node and input node of the amplifier. The feedback network includes a feedback circuit path with a feedback impedance that provides feedback signal to the input node. This feedback mechanism compensates for the abrupt phase changes around the tank circuit's resonance frequency, enabling input impedance matching to be achieved despite the phase variations caused by the high Q tank circuit.
2Power
If maximum gain and impedance matching are optimized at different frequencies, then each parameter can be maximized, but the amplifier cannot achieve both simultaneously at the same frequency
Solution Approach 1:
The patent employs dynamic tuning capabilities through varactor diodes connected to the tank circuit and feedback network. These varactor diodes can be controlled by tuning voltages to adjust the capacitance values dynamically, allowing the resonant frequency of the tank circuit and the feedback network to be tuned simultaneously. This dynamic adjustment enables both maximum gain and impedance matching to be optimized at the same operating frequency, resolving the contradiction between maximizing individual parameters at different frequencies.
3Ease of operation
If high Q components are used to achieve good impedance matching, then impedance matching performance is improved, but manufacturing cost and complexity increase
Solution Approach 1:
The patent uses standard components with relatively low Q values (such as conventional capacitors and resistors) in the feedback network instead of requiring high Q components. The feedback mechanism compensates for the Q limitations, allowing good impedance matching to be achieved with cheaper, easier-to-manufacture components. This approach trades the need for expensive high Q components for a feedback-based solution that uses readily available, cost-effective parts.
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
This approach enables simultaneous optimization of gain and input impedance matching at the same frequency, facilitating cost-effective and efficient design with components that are easier and cheaper to manufacture, while maintaining stability and high gain performance.
Implementation Method 1
a tunable tank circuit, such as an LC circuit, connected to an output node of the amplifier. Such a tank circuit can provide a desired degree of frequency selectivity
Implementation Method 2
a feedback network between the output node and an input node. Such a feedback network can facilitate in providing input impedance matching
Implementation Method 3
connecting a tunable capacitor between an internal node of the feedback circuit path and a reference voltage node
Data Source
AI summary
An amplifier for a receiver circuit is disclosed. The amplifier has an input node (Vin) and an output node (Vout). It comprises a tunable tank circuit connected to the output node (Vout), a feedback circuit path connected between the output node (Vout) and the input node (Vin), and a tunable capacitor connected between an internal node of the feedback circuit path and a reference-voltage node. A receiver circuit and a communication apparatus is disclosed as well.