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The noise factor is defined as the ratio of the output noise power of a device to the portion thereof attributable to thermal noise in the input termination at standard noise temperature T 0 (usually 290 K). The noise factor is thus the ratio of actual output noise to that which would remain if the device itself did not introduce noise, which ...
The noise factor (a linear term) is more often expressed as the noise figure (in decibels) using the conversion: = The noise figure can also be seen as the decrease in signal-to-noise ratio (SNR) caused by passing a signal through a system if the original signal had a noise temperature of 290 K. This is a common way of expressing the noise ...
Here, k ≈ 1.38 × 10 −23 J/K is the Boltzmann constant and kT 0 is the available noise power density (the noise is thermal noise, Johnson noise). As a numerical example: A receiver has a bandwidth of 100 MHz , a noise figure of 1.5 dB and the physical temperature of the system is 290 K .
where is the overall noise factor of the subsequent stages. According to the equation, the overall noise factor, F r e c e i v e r {\displaystyle F_{\mathrm {receiver} }} , is dominated by the noise factor of the LNA, F L N A {\displaystyle F_{\mathrm {LNA} }} , if the gain is sufficiently high.
where f 0 is the output frequency, Q l is the loaded quality factor, f m is the offset from the output frequency (Hz), f c is the 1/f corner frequency, F is the noise factor of the amplifier, k is the Boltzmann constant, T is absolute temperature, and P s is the available power at the sustaining amplifier input. [3]
The Y-factor method is a common measurement technique for this purpose. [1] By using a noise diode, the output noise of an amplifier is measured using two input noise levels, and by measuring the output noise factor (referred to as Y) the noise figure of the amplifier can be determined without having to measure the amplifier gain.
The ratio of (a) total received power, i.e., the signal to (b) the noise-plus-distortion power. This is modeled by the equation above. [2] The ratio of (a) the power of a test signal, i.e. a sine wave, to (b) the residual received power, i.e. noise-plus-distortion power. With this definition, it is possible to have a SINAD level less than one.
If the noise current contribution i n R s >> noise voltage e n, then reducing the source impedance by a factor of 4 reduces the i n contribution by a factor of 4 while the source's thermal noise voltage declines by factor of 2 (ideal transformer with 2:1 turns ratio gives the 4:1 Z ratio); SNR improves by 6 dB. But there's another issue.