Differential Cascode LNA With Tuned Impedance Matching
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Solution Overview
Problem
Existing low-noise amplifiers (LNAs) face challenges in achieving matched input and output impedances over a range of frequencies while minimizing noise addition, often requiring a large number of components or using resistors that introduce thermal noise.
Innovation Solution
The design incorporates a frequency-selective network using a parallel connection of an inductor and capacitor to set both input and output impedances equal to the characteristic impedance of the transmission line, reducing noise figure by canceling current noise and achieving matched impedances with a smaller component count.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If resistors are used as part of the impedance matching network, then impedance matching is achieved, but thermal noise is added to the signal
Solution Approach 1:
The patent removes resistors from the impedance matching network entirely, extracting the harmful noise-generating component while preserving the impedance matching function through an alternative approach using only reactive components (inductors and capacitors) in a transformer coupling configuration.
Solution Approach 2:
The patent combines the impedance matching function with the signal coupling function by using a transformer structure where the primary and secondary windings serve both to transfer the signal and to provide impedance transformation, eliminating the need for separate resistor-based matching networks.
2Reliability
If a large number of components are used to provide tuned input and output impedances, then impedance matching over a frequency range is achieved, but device complexity increases
Solution Approach 1:
The transformer structure serves multiple functions simultaneously: it provides impedance transformation for both input and output matching, acts as a signal coupling element, and provides frequency selectivity through its inherent inductive properties, thereby reducing the need for separate tuned circuits for each function.
Solution Approach 2:
The patent merges the functions of impedance matching and frequency selection into a single transformer-based network, where the transformer windings and associated capacitors work together to provide both impedance transformation and frequency-dependent behavior, reducing the total component count compared to separate networks for each function.
3Reliability
If traditional impedance matching networks are used, then matched input and output impedances are achieved, but noise figure increases due to thermal effects
Solution Approach 1:
The patent extracts and removes all resistive elements from the impedance matching network, eliminating the source of thermal noise while maintaining impedance matching capability through purely reactive transformer coupling that preserves signal integrity without thermal degradation.
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 results in a low-noise amplifier with reduced noise figure and matched input and output impedances across the desired frequency band, using fewer components and minimizing thermal noise generation.
Implementation Method 1
The amplifier includes a frequency-selective network. The frequency-selective network is connected between the first one of the pair of output terminals and the second one of the pair of output terminals
Implementation Method 2
The design incorporates a frequency-selective network using a parallel connection of an inductor and capacitor
Data Source
AI summary
A low-noise amplifier (LNA) includes a pair of transistors connected in a cascode configuration to provide amplification to an input signal. The LNA generates an amplified output in differential form across a pair of output terminals. One of the pair of output terminals is the output node of the cascode configuration. The LNA further includes a feedback transistor with its gate terminal connected to the output node of the cascode configuration and its drain terminal connected to the other one of the pair of output terminals. The differential nature of the amplified output reduces the noise figure of the LNA. A frequency-selective network connected across the pair of output terminals sets the frequency selectivity of each of the input section and the output section of the LNA.