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input device noise figure and input device noise figure

Lecture



It is necessary to distinguish the noise figure of the input device itself and the noise figure of the input device and the first receiver stage, which are determined jointly. We first consider the latter case as more general, and then as a particular case, we determine the noise factor of the input device itself.

The noise ratio of the input circuit taking into account the first cascade of the receiver.

When calculating the noise figure, the antenna noise as a signal source, the noise of the input device itself and the noise of the first stage, counted at its input, are taken into account.

Suppose that the conductance of the signal source recalculated to the input of the first stage is

input device noise figure and input device noise figure ,

and its own noises are characterized by noise current.

input device noise figure and input device noise figure .

Conductivity of the resonant circuit

input device noise figure and input device noise figure ,

counted to the input of the first cascade, causes the appearance of noise current

input device noise figure and input device noise figure .

The noise of an electronic device standing at the entrance is recalculated to its input and is characterized by the source of the noise.

input device noise figure and input device noise figure ,

Where input device noise figure and input device noise figure - noise resistance.

Obviously, it is also necessary to take into account the noise that appears in the input conductivity of the electronic device, and these noises are represented by noise current.

input device noise figure and input device noise figure ,

Where input device noise figure and input device noise figure - relative noise temperature of noise, which shows how many times the noise of the real input conductance is greater than the noise of the corresponding ohmic resistance.

Values input device noise figure and input device noise figure and input device noise figure and input device noise figure is given in reference books or calculated using formulas known from the course of electronic devices. The value of P represents the effective noise bandwidth of the receiver. Given the above about the sources of noise, the equivalent noise scheme can be represented as follows.

input device noise figure and input device noise figure

Figure 6.6.

As can be seen in the conductivity figure input device noise figure and input device noise figure , input device noise figure and input device noise figure , input device noise figure and input device noise figure are respectively sources of noise input device noise figure and input device noise figure , input device noise figure and input device noise figure , input device noise figure and input device noise figure and the amplification device - the source of noise input device noise figure and input device noise figure

The noise figure of the system, in accordance with the definition, can be represented as a ratio of signal power and noise in the antenna and at the output of the circuit, i.e.

input device noise figure and input device noise figure .

The signal-to-noise ratio in the antenna as the source is determined by its data. In particular, the nominal power of the antenna as a signal source and noise source

input device noise figure and input device noise figure ; input device noise figure and input device noise figure .

Their attitude is

input device noise figure and input device noise figure .

We now find the signal-to-noise ratio at the output.

The nominal signal power and output noise are respectively

input device noise figure and input device noise figure ; input device noise figure and input device noise figure ,

Where

input device noise figure and input device noise figure .

- the resulting conductivity of noisy sources.

Find the noise voltage at the terminals 4-4 "

input device noise figure and input device noise figure ,

Where

input device noise figure and input device noise figure

or

input device noise figure and input device noise figure .

Considering the values input device noise figure and input device noise figure , input device noise figure and input device noise figure , input device noise figure and input device noise figure the total noise voltage at the output of the circuit

input device noise figure and input device noise figure .

The expression in square brackets is the resulting noise resistance of the input device and the first cascade:

input device noise figure and input device noise figure .

Three members of this sum characterize the noise properties of the following sources:

a) the input device itself, whose noise properties are determined by the resistance recalculated to the input of the first stage, i.e. by size

input device noise figure and input device noise figure .

b) the input of the first stage, the noise properties of which are determined by additional noise in the input resistance of the electronic device

input device noise figure and input device noise figure ;

c) an amplifier device, whose noise properties are determined by noise resistance input device noise figure and input device noise figure .

We now determine the signal-to-noise ratio at the output of the circuit.

input device noise figure and input device noise figure .

Then the noise figure

input device noise figure and input device noise figure .

Providing the required modes when choosing the connection between the antenna, the loop and the input of the first stage.

Let us consider in more detail the expression for the noise figure, substituting in it the value of the resulting noise resistance:

input device noise figure and input device noise figure .

Taking into account that

input device noise figure and input device noise figure .

Where input device noise figure and input device noise figure - recalculated to the input of the first cascade load conductance.

input device noise figure and input device noise figure .

Noise figure can be written

input device noise figure and input device noise figure .

The second term characterizes the additional value of W due to the circuit noise and the input of the first cascade.

The third term characterizes the additional value W at the expense of an electronic device.

Analyzing the last expression, we consider 3 particular cases of choosing the connection between the antenna, the input circuit and the input of the first cascade:

but) the first particular case is the power matching mode , in which the matching is performed at the receiver input, i.e. transformation ratio (inclusion) input device noise figure and input device noise figure is taken equal to the matching value input device noise figure and input device noise figure Because in negotiation mode input device noise figure and input device noise figure then the noise figure is determined

input device noise figure and input device noise figure .

In the region of relatively high frequencies, when

input device noise figure and input device noise figure , input device noise figure and input device noise figure ,

noise figure

input device noise figure and input device noise figure ,

those. determined by the values input device noise figure and input device noise figure and input device noise figure and input device noise figure . From this it follows that in order to reduce the noise figure, it is necessary to choose electronic devices with the lowest possible values. input device noise figure and input device noise figure and input device noise figure and input device noise figure .

b) The second special case is the noise matching mode .

This case is characterized by the fact that the inclusion coefficient from the antenna input device noise figure and input device noise figure , as in the previous case, is taken equal to the matching value, i.e. input device noise figure and input device noise figure and mismatch factor input device noise figure and input device noise figure .

At the same time, the contour is connected to the input of the first cascade not arbitrarily, but in a quite definite way, by choosing some optimal value of the switching coefficient. input device noise figure and input device noise figure in order to reduce the noise figure.

The expression for the noise figure given that input device noise figure and input device noise figure take the form

input device noise figure and input device noise figure ,

In order to find the optimal value of the coefficient of inclusion in terms of noise figure input device noise figure and input device noise figure take the derivative input device noise figure and input device noise figure by input device noise figure and input device noise figure and equate it to zero.

From here

input device noise figure and input device noise figure .

Then

input device noise figure and input device noise figure ,

those. noise factor is determined only by the parameters of the electronic device.

A decrease in the noise figure due to incomplete connection of the circuit to the input of the first cascade is due to the action of two factors: a decrease in the recalculated value of the resonant resistance of the circuit input device noise figure and input device noise figure , resulting in a sharp decrease in noise level (in proportion to input device noise figure and input device noise figure ), and at the same time reducing the level of the useful signal removed from the contour input device noise figure and input device noise figure (proportionally input device noise figure and input device noise figure ).

at) the third special case is the mode of optimal noise mismatch .

In this case, the coefficient input device noise figure and input device noise figure from the side of the antenna is not taken equal to the matching value, but its optimal value is found input device noise figure and input device noise figure (or input device noise figure and input device noise figure ), at which the noise figure gets the minimum value input device noise figure and input device noise figure .

For determining input device noise figure and input device noise figure we write W in the form

input device noise figure and input device noise figure .

Take the derivative of this expression for a input device noise figure and input device noise figure , we equate it to zero and find

input device noise figure and input device noise figure .

Then

input device noise figure and input device noise figure .

In the region of relatively high frequencies, when input device noise figure and input device noise figure , size input device noise figure and input device noise figure and

input device noise figure and input device noise figure .

those. noise factor is determined only by the parameters of the electronic device.

Decrease in noise figure at input device noise figure and input device noise figure is achieved by reducing the influence of the noise of the resonant circuit and the cascade input.

input device noise figure and input device noise figure

Figure 6.7.

The noise figure of the input device without taking into account the influence of the first cascade.

As already shown

input device noise figure and input device noise figure ; input device noise figure and input device noise figure .

For the input device without taking into account the influence of the first cascade

input device noise figure and input device noise figure ,

input device noise figure and input device noise figure .

Attitude

input device noise figure and input device noise figure .


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Devices for the reception and processing of radio signals, Transmission, reception and processing of signals

Terms: Devices for the reception and processing of radio signals, Transmission, reception and processing of signals