Switched-Capacitor LNA With Feedback Inductor for Frequency Stability
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Solution Overview
Problem
Traditional receiver front-ends require bulky and expensive external SAW filters, which are not suitable for high frequencies like 802.11ac WLAN, and suffer from parasitic effects that shift the working frequency downwards, especially above 3 GHz.
Innovation Solution
A low noise amplifier with a feedback inductor connected in parallel to the inverter and switched-capacitor units, which balances the parasitic capacitors' effect, maintaining the working frequency at the center frequency of the switched-capacitor units and correcting frequency offset.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If SAW filters are used to filter out-of-band blockers and interferences, then filtering performance is improved, but device size, cost, and flexibility deteriorate
Solution Approach 1:
The patent combines the filtering function with the LNA circuit by integrating switched-capacitor units and feedback inductors directly into the amplifier circuit. This merging eliminates the need for separate external SAW filters, achieving both size reduction and maintained filtering performance through the integrated frequency selectivity mechanism.
2Volume of moving object
If SAW filters are replaced with integrated circuits, then device size and cost are reduced, but frequency stability deteriorates due to parasitic effects
Solution Approach 1:
The patent employs feedback inductors connected in parallel with the switched-capacitor units to create a feedback mechanism that compensates for parasitic capacitance effects. This feedback structure stabilizes the resonant frequency by counteracting the frequency downward shift caused by parasitic elements, thereby maintaining frequency stability in the integrated circuit.
Solution Approach 2:
The patent changes the electrical parameters of the circuit by introducing adjustable switched-capacitor units that can be configured to compensate for parasitic effects. By dynamically adjusting the capacitance values through switching networks, the circuit maintains accurate frequency operation despite parasitic capacitance variations.
3Device complexity
If conventional integrated LNA circuits are used above 3 GHz, then integration is improved, but frequency accuracy deteriorates due to parasitic capacitance
Solution Approach 1:
The patent introduces feedback inductors as intermediary elements that mediate between the switched-capacitor units and the parasitic capacitance effects. These inductors act as compensating elements that counterbalance the parasitic capacitance, thereby maintaining frequency accuracy in the highly integrated LNA circuit operating above 3 GHz.
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 allows the low noise amplifier to operate at high frequencies with improved performance, reducing noise figure and center-frequency offset, and enhancing signal-to-noise ratio by around 0.2 dB.
Implementation Method 1
due to ubiquitous parasitic effects, especially parasitic capacitance, the actual working frequency will not be the same as desired. Especially when working at higher frequencies, the working frequency will be shifted downwards a lot
Implementation Method 2
The feedback inductor is electrically connected with the inverter in parallel. The affection of the parasitic capacitors is balanced by the feedback inductor
Implementation Method 3
Each of the plural switched-capacitor units is electrically connected with the inverter in parallel and includes a switch and a capacitor connected in series
Data Source
AI summary
A low noise amplifier is provided. The low noise amplifier includes an input port, an output port, an inverter, a plurality of switched-capacitor units and a feedback inductor. The inverter is electrically connected between the input port and the output port. Each of the plural switched-capacitor units is electrically connected with the inverter in parallel and includes a switch and a capacitor connected in series. The feedback inductor is electrically connected with the inverter in parallel.