Task 7.
7. Determine the noise coefficient of the amplifier device in dB if its effective noise temperature (100 + Nstudent*2.0) K.
7.1. Calculate the effective noise temperature of two such devices connected in cascade if the gain of each device (10+ Ngroup *0.5) dB.
7.2 Analyze the result
7. Determine the noise coefficient of the amplifier.
To do this, use the formula:
;
Where
;
We get:
For the temperature
,
we will take the standard value of 300 K.
7.1 Calculate the effective noise temperature of two such devices connected in cascade if the gain of each device is 10.5 dB.
To solve this calculation, we can use Frie’s formula: formula:
Since there are only 2 amplifying stages, the formula will take the form:
is the increase factor of the
i element
Since the instruments are the same, then NF1 = NF2 = NF, G1 = G2 = G:
To solve previous equation, we should find G:
Calculation of the effective noise temperature:
7.2 During the transformations, it turned out that the noise factor of the first element plays a decisive role in the cascade inclusion, since the effect of its gain on the noise of the subsequent element of the cascade is visible.
Task 8.
8. What is the difference between the introduction of the concepts of "effective" noise temperature and "effective" noise resistance?
8.1. Explain the introduction of the concepts of "white" and "color" noise.
8.2. Determine the average noise fluctuation of the current at
T=(300+ Nstudent) K.
8. To begin with, consider the Van der Zyl formula:
This formula determines the
average square of the noise current that arises due to the diffusion
of D(
)
charged particles in the resistor elements with a temperature
in the frequency bandff. If we consider the case of thermodynamic
equilibrium, then the Van der Zyl formula turns into the Nyquist
formula:
This formula is for an idealized case, since in reality electric fields change the energy of electric charges, and therefore the amount of noise. The Nyquist formula can be obtained for the case of disequilibrium by using the concepts of effective noise temperature and effective noise conductivity:
– the noise ratio, which
shows how much the device makes more noise than according to the
Nyquist formula. Nyquist formula for the case of disequilibrium:
8.1 Noise is an unwanted (accidental) valid signal distortion. The fundamental sources of noise are energy dissipation and discrete electron charge. Noises limit the functionality of radio electronic devices because against their background it is difficult to isolate the valid signal if the noise power greatly exceeds the signal power.
White noise is a random signal having the same intensity at different frequencies, giving it a constant spectral power density.
The current dispersion is determined by the Schottky formula:
Color noise is noise whose spectrum depends on frequency, that is, the spectral power density differs depending on frequency. Depending on the change in the spectrum at different frequencies, noise can be assigned a color.
8.2
Let R = 5000 om,
According to the Nyquist formula:
Answer:
