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A low-noise amplifier (LNA) is an electronic component that amplifies a very low-power signal without significantly degrading its signal-to-noise ratio (SNR). Any electronic amplifier will increase the power of both the signal and the noise present at its input, but the amplifier will also introduce some additional noise.
An RF amplifier, often called the low-noise amplifier (LNA). Its primary responsibility is to increase the sensitivity of the receiver by amplifying weak signals without contaminating them with noise, so that they can stay above the noise level in succeeding stages. It must have a very low noise figure (NF). The RF amplifier may not be needed ...
The f c for an amplifier depends on the actual configuration used, because radio-frequency and low-frequency negative feedback can have an effect on f c. So for accurate results, f c must be determined from added noise measurements on the amplifier using R.F., with the actual circuit configuration to be used in the oscillator.
The low-noise quality of an LNB is expressed as the noise figure (or sometimes noise temperature). This is the signal-to-noise ratio at the input divided by the signal-to-noise ratio at the output. It is typically expressed as a decibels (dB) value. The ideal LNB, effectively a perfect amplifier, would have a noise figure of 0 dB and would not ...
There are a number of RF amplifier tubes that operate in a similar fashion to the TWT, known collectively as velocity-modulated tubes. The best known example is the klystron. All of these tubes use the same basic "bunching" of electrons to provide the amplification process, and differ largely in what process causes the velocity modulation to occur.
Parametric amplifiers are used in applications requiring extremely low noise. A parametric oscillator is a driven harmonic oscillator in which the oscillations are driven by varying some parameters of the system at some frequencies, typically different from the natural frequency of the oscillator.
The noise power at the output of the amplifier chain consists of four parts: The amplified noise of the source ( N i ⋅ G 1 G 2 G 3 {\displaystyle N_{i}\cdot G_{1}G_{2}G_{3}} ) The output referred noise of the first amplifier N a 1 {\displaystyle N_{a1}} amplified by the second and third amplifier ( N a 1 ⋅ G 2 G 3 {\displaystyle N_{a1}\cdot ...
The first amplifier in a chain usually has the most significant effect on the total noise figure because the noise figures of the following stages are reduced by stage gains. Consequently, the first amplifier usually has a low noise figure, and the noise figure requirements of subsequent stages is usually more relaxed.