Low-noise Amplifier for a sensitive radio receiver

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SUMMARY

The discussion focuses on designing a low-noise amplifier (LNA) for sensitive radio receivers, emphasizing key noise sources such as thermal noise, shot noise, and flicker noise at the transistor level. Various LNA topologies, including common-source, common-gate, and common-drain with inductive degeneration, significantly influence the overall noise figure and gain. The conversation highlights the importance of impedance matching and techniques like "Star Grounding" to minimize noise coupling in PCBAs. Understanding these factors is crucial for optimizing receiver sensitivity and performance.

PREREQUISITES
  • Understanding of low-noise amplifier (LNA) design principles
  • Familiarity with noise sources in electronics, including thermal noise and shot noise
  • Knowledge of LNA topologies such as common-source and common-drain
  • Experience with PCB design and grounding techniques
NEXT STEPS
  • Research the impact of different LNA topologies on noise figure and gain
  • Learn about impedance matching techniques using the Smith chart
  • Explore advanced grounding techniques like "Star Grounding" for sensitive circuits
  • Investigate receiver sensitivity measurement methods and standards
USEFUL FOR

Electronics engineers, radio frequency (RF) designers, and hobbyists involved in building or optimizing low-noise amplifiers for sensitive radio applications.

WonderNomad
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I'm designing a low-noise amplifier (LNA) for a sensitive radio receiver. What are the key noise sources I need to consider at the transistor level (e.g., thermal noise, shot noise, flicker noise)? How do different LNA topologies (e.g., common-source, common-gate, common-drain with inductive degeneration) impact the overall noise figure and gain? What are the trade-offs involved in optimizing these parameters?
 
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In addition to the buy-vs-build question asked by @Baluncore -- do you have experience designing PCBAs with sensitive radio circuits? What is the application? Will there be digital electronics on the same PCBA? It is *extremely* important to isolate different parts of radio circuits on PCBAs to avoid coupling of noise between sections via shared impedances (like power supply and ground impedance). Are you familiar with techniques such as "Star Grounding" to achieve such isolation?

Also, what level of receiver sensitivity (in dBm) are you shooting for? https://www.repeater-builder.com/tech-info/measuring-sensitivity/measuring-sensitivity.html
 
I was wondering why you have chosen inductive degeneration for common source operation?
 
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It’s all about matching the source impedance to the transistor input impedance that optimizes its noise figure. Pay attention to the Smith chart noise figure circles on the device data sheet.
 

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