Low-Noise Amplifier Path Switching for Stable Input Impedance
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Solution Overview
Problem
Low noise amplifier circuits face challenges in maintaining noise characteristics when switching between paths that do and do not include the LNA, particularly in environments with overlapping signal channels, leading to signal saturation and distortion.
Innovation Solution
A low noise amplifier circuit design with multiple paths, including a MOS transistor, inductors, capacitors, and a changeover switch, where a selector switches between paths to prevent noise characteristic deterioration by controlling the changeover switch's state based on signal levels, ensuring input impedance remains optimal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a detour path is provided in parallel with the LNA path to handle high signal levels, then signal saturation is prevented, but the noise characteristic deteriorates due to switch circuit resistance
Solution Approach 1:
A bypass switch is introduced as an intermediary element that can selectively connect or disconnect the detour path. When the LNA operates normally, the bypass switch disconnects the detour path to avoid noise. When signal saturation is detected, the bypass switch connects the detour path to prevent saturation, thus mediating between noise prevention and saturation prevention
Solution Approach 2:
The circuit dynamically switches between the LNA path and the detour path based on signal level conditions. The bypass switch changes its state (connected or disconnected) according to whether the signal level exceeds a threshold, making the circuit configuration adaptive to different operating conditions
2Adaptability or versatility
If the LNA is designed for wide band reception, then adaptability to various countries and regions is improved, but the noise characteristic deteriorates due to narrow optimal band constraints
Solution Approach 1:
The LNA is divided into multiple independent transistor units (first through fourth NMOS transistors), each optimized for specific frequency bands. By segmenting the amplification function across multiple units, the circuit can select appropriate transistors for different bands, achieving wide band coverage while maintaining optimal noise characteristics for each segment
Solution Approach 2:
Each NMOS transistor unit has locally optimized characteristics suited for specific frequency ranges. The first and second transistors are optimized for lower bands while the third and fourth are optimized for higher bands, allowing each component to operate in its optimal performance zone
3Adaptability or versatility
If input NMOS transistor groups are switched on and off to generate signals from different output paths, then signal level adaptability is improved, but input impedance matching becomes difficult to maintain
Solution Approach 1:
Multiple NMOS transistor units are merged into a single LNA circuit structure with shared input and output nodes. The parallel configuration of transistor units allows signal level adaptability while their combined input impedance can be designed to maintain 50Ω matching across different operating states
Solution Approach 2:
The circuit utilizes parameter changes in transistor operating states (on/off, saturation/linear regions) to achieve different output paths while the overall input impedance is designed to remain relatively constant through proper biasing and circuit topology
Data Source
AI summary
An LNA circuit includes: paths provided between an input and an output terminals, an LNA provided in at least one path, and a selector selecting one path. The LNA includes: a MOS transistor coupled between a first and a second power supplies, a first inductor coupled to a source of the MOS transistor, a capacitor formed between a gate and the source of the MOS transistor, a second inductor coupled between the gate of the MOS transistor and the input terminal, and a changeover switch coupled parallelly with at least one of the capacitor, and the first and the second inductors. The selector switches between a first state that one path is selected and the changeover switch is on, and a second state that another path is selected and the changeover switch is off. Alternatively, the one path and the another path are respectively provided without and with the LNA.