(provide gain with little added noise of their own) and are not suitable for non-LNA applications. One example is Skyworks Solutions’ SKY67180-306LF, a two- stage, high-gain LNA for 1.5 to 3.8 gigahertz (GHz) applications such as cellular repeaters and small/ macro-cell sites for LTE, GSM, and WCDMA applications, as well as S-band and C band ultra-low-noise receivers (Figure 2). The first stage of this 16-lead QFN device uses GaAs pHEMT transistors for an ultra-low noise figure (NF), while the output stage (heterojunction bipolar transistors) provides additional gain at that frequency, along with high linearity and efficiency. The result is an LNA
with a noise floor (NF) of 0.8 dB and 31 dB gain at 3.5 GHz. Another critical issue is where to physically place the LNA; it’s obviously easier to put it with the rest of the receiver circuitry. However, this means that the unavoidable thermal noise of the cable carrying the amplified signal from the LNA to the system will be added to the unamplified signal, further reducing SNR. For this reason, even consumer applications such as very small aperture terminal (VSAT) satellite dishes put the LNA right at the focal point of the dish.
Conclusion Although antenna transmitter and receiver functions adhere to the principle of reciprocity, their actual challenges diverge. For many RF antenna situations, a dedicated LNA is often the best or only way to boost the received signal level to a usable value while having minimal impact on SNR. Specialized LNAs are available that are tailored to specific frequency bands and with gain values that can resolve the signal level/SNR dilemma.
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References
1. “Get the Most Out of Exotic Processes for 5G LNAs” https://www.digikey.com/en/ articles/get-the-most-out-of- exotic-processes-for-5g-lnas 2. “Understanding the Basics of Low-Noise and Power Amplifiers in Wireless Designs” https://www.digikey.com/en/ articles/understanding-the- basics-of-low-noise-and-power- amplifiers-in-wireless-designs 3. “Low-Noise Amplifiers Maximize Receiver Sensitivity” https://www.digikey.com/en/ articles/low-noise-amplifiers- maximize-receiver-sensitivity
1. Increase Broadband Speed, “Wi- Fi Setup Guide: What is a Good Signal Level or Signal-to-Noise Ratio (SNR) for Wi-Fi? ” 2. Nordic Semiconductor, “GPS functionality test ” 3. The Great Courses Daily, “ Voyager 2” Sends Messages from Interstellar Space with Minimal Signal ” 4. National Radio Astronomy Observatory, “How Strong is the Signal from the Voyager 1 Spacecraft When it Reaches Earth?” 5. IEEE Communications Society, “ Voyager - A Space Exploration Mission Like No Other ”
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