Profit (electronic)

See also: Profit

In electronic, the profit indicates the capacity of an electronic circuit to increase the power or the amplitude of a signal. The profit is generally calculated by carrying out the ratio of the output signal on that of entry.

Used only, the term of “profit” is ambiguous because it is not known if it refers to a profit in tension, running or power.

Profit and decibel

The profit G in power of an assembly is calculated in the following way:

$G=10\; \backslash \; log\; \backslash \; left\; (\{\backslash \; frac\; \{P\_\; \{S\}\}\; \{P\_\; \{E\}\}\}\; \backslash \; right)\; \backslash \; \backslash \; mathrm\; \{dB\}$

With P_e and P_s respectively powers of entry and exit.

By using the Law of Ohm, the preceding formula can be rewritten according to the tensions of entry and exit V_e and V_s as well as resistance of R_e entry of the assembly and as well as resistance of R_s load.

$G=10\; \backslash \; log\; \{\backslash \; frac\; \{(\backslash \; frac\; \{R\_\; \{S\}\})\}\{(\backslash \; frac\; \{R\_\; \{E\}\})\}\}\; \backslash \; \backslash \; mathrm\; \{dB\}$

If the circuit is adapted in impedance (R_s= R_e), this expression becomes:

$G=10\; \backslash \; log\; \backslash \; left\; (\{\backslash \; frac\; \{V\_\; \{S\}\}\; \{V\_\; \{S\}\}\}\; \backslash \; right)\; ^2\; \backslash \; \backslash \; mathrm\; \{dB\}$

maybe with the final one:

$G=20\; \backslash \; log\; \backslash \; left\; (\{\backslash \; frac\; \{V\_\; \{S\}\}\; \{V\_\; \{E\}\}\}\; \backslash \; right)\; \backslash \; \backslash \; mathrm\; \{dB\}$

It is this formula which is used to calculate the profit in tension of an assembly. This convention allows, in the assemblies where the impedance of entry is equal to the output impedance, to measure the three profits (in intensity, tension, and power) by the same number.

To qualify an assembly, one often speaks about profit in term of strong or weak profit. A strong profit will mean that one will have a value of more important exit compared to that of entry. And conversely for a weak profit.

Study of the profit

The profit of an assembly can vary according to the frequency. It is the case for the filters because they attenuate certain components of a signal and let some pass from others. In order to study the frequential behavior of the profit of a filter or any electronic assembly, one can use graphic tools such as the Diagramme of Bode or the Diagramme of Nyquist.

The profit represents in fact the role of the filter. The larger the profit is for a given frequency F, the less the signals of this frequency are attenuated. On the contrary, more the profit is weak, more the signal is attenuated, even inhibited.

Profit of a bipolar transistor

The profit of a bipolar Transistor is the relationship between: the current circulating in its base and the current circulating in its collecting, in mode known as linear (unsaturated). This profit is often indicated by the letter β (or h₂₁). The profit depends on the construction of the transistor, it varies with: the collector current, the tension transmitter-collector, the frequency of use and the temperature. The profit can vary in significant proportions within the same batch.

One calls frequency of transition the frequency to which the profit is worth 1, i.e. the frequency beyond which the transistor does not amplify any more.

In general, the transistors of power have a profit weaker than the transistors of weak signal. A Transistor Darlington has a profit more raised. Typically a bipolar transistor has a profit ranging between 50 and 300.

Internal bonds

Amplifying S

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