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Low Noise Amplifier(LNA) Basics

Low noise amplifier (LNA) is an electronic amplifier, which amplifies but does not significantly reduce its very low power signal-to-noise ratio.

What is Low Noise Amplifier(LNA)

The amplifier will increase the signal power and input noise, but the amplifier will also introduce some additional noise. LNA is designed to minimize this extra noise. Designers can minimize additional noise by selecting low noise components, work points, and circuit topologies. Minimizing extra noise must be balanced with other design objectives such as power gain and impedance matching.

LNA exists in radio communication system, medical instrument and electronic test equipment. A typical LNA can provide 100 (20 dB) power gain while reducing the signal-to-noise ratio by less than twice (3 dB noise factor (NF)). Although LNA mainly focuses on the weak signal just above the background noise, they must also consider the existence of large signal that will cause intermodulation distortion.

The function of Low Noise Amplifier

Noise amplifier (LNA) is mainly designed for base station applications of mobile communication infrastructure, such as transceiver wireless communication card, tower top amplifier (TMA), combiner, repeater and remote / digital wireless broadband head end equipment. It also sets a new benchmark for NF (noise figure).

At present, the wireless communication infrastructure industry is facing the challenge of providing the best signal quality and coverage in the congested spectrum. Receiver sensitivity is one of the most critical requirements in the design of base station receiving path. Appropriate LNA selection, especially the first level LNA, can greatly improve the sensitivity performance of base station receiver, and low noise index is also the key design goal. Avago has proposed The best noise index of 0.48db product at 1900MHz is provided.

Another key design is linearity, which affects the receiver’s ability to distinguish close approach signals and false signals. The third-order cutoff OIP3 can be used to define linearity. Under the typical operating conditions of 1900MHz and 5V / 51ma, Avago’s unique GaAs enhanced mode PHEMT technology can bring 0.48db noise index and 35dbm OIP3. Under the typical operating conditions of 2500mhz and 5V / 56ma, Avago’s unique GaAs enhanced mode PHEMT technology can bring 0.48db noise index and 35dbm OIP3, The noise index is 0.59db, OIP3 is 35dbm. With low noise index and high OIP3, these new low noise amplifiers of Avago can provide a larger design space for base station receiver path than existing amplifier products. Adjustable capability and common pin arrangement lead to design optimization and flexibility.

Principle of low noise amplifier

Low noise amplifier, a low noise amplifier. Generally, it is used as the preamplifier of high frequency or intermediate frequency of various radio receivers and the amplifier circuit of high sensitivity electronic detection equipment. In the case of amplifying weak signal, the noise of the amplifier itself may cause serious interference to the signal, so we hope to reduce the noise and improve the signal-to-noise ratio of the output.

What is the function of low noise amplifier when making a phone call?

Most of the modern low noise amplifiers are transistors and field effect transistors, while the microwave low noise amplifiers are varactor diode parametric amplifiers. The noise temperature at room temperature can be lower than tens of degrees (absolute temperature), and the cooling parametric amplifiers can be lower than 20K. GaAs FET low noise microwave amplifiers have been widely used, and their noise coefficients can be Less than 2 dB. The noise coefficient of the amplifier is also related to the operation state of the transistor and the internal resistance of the source. When the operating frequency and internal resistance of the source are given, the noise coefficient is also related to the DC operating point of the transistor. In order to meet the requirements of low noise and high gain, a low noise amplifier with common emitter and common base cascade is often used.

An amplifier with a low noise figure. Generally, it is used as the preamplifier of high frequency or intermediate frequency of various radio receivers and the expansion circuit of high sensitivity electronic detection equipment. In the case of expanding weak and small signal, the noise of amplifier itself may disturb the signal seriously, so it is expected to reduce this noise to improve the output signal-to-noise ratio. The signal-to-noise ratio (SNR) degradation caused by amplifiers is usually represented by the noise factor F. The noise factor F of the ideal amplifier is 1 (0 dB), which means that the output SNR is equal to the input SNR.

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