How do you understand the frequency characteristics of a transistor?

Semiconductor transistors.

When used for AC amplification, the current amplification factor is frequency-dependent. When the operating frequency of the transistor is low, the HFE value does not change much, but when the transistor is used in a high-frequency circuit, the current amplification coefficient will continue to decrease with the increase of the operating frequency, and the frequency characteristic parameters need to be considered. The frequency characteristic parameters are mainly as follows.

1) Common base cut-off frequency.

f Common base cutoff frequency is also called cutoff frequency. In a common base circuit, the current amplification factor value. It is basically a constant at lower operating frequencies.

2) The common emitter cut-off frequency f f and f have the following relationship: (3) the characteristic frequency ft diagram shows the frequency characteristics of the semiconductor triode (4) the maximum oscillation frequency fm The definition of the maximum oscillation frequency is: when the power gain of the semiconductor triode is equal to 1, the frequency is called the maximum oscillation frequency fm of the semiconductor triode.

When the working frequency is greater than fm, the triode cannot get power amplification; When the operating frequency is lower than fm, the transistor can get power amplification. It can be seen that FM is an important parameter of semiconductor transistors.

When the frequency is high, the current amplification of the transistor decreases due to the junction capacitance, etc., and the frequency characteristic curve expresses this relationship. There is also a frequency characteristic parameter called unit gain bandwidth, which refers to the frequency when the current gain of the triode drops to 1, and when it is higher than this frequency, the transistor completely loses the current amplification.

The triode will reduce the circuit amplification in both the low frequency band and the high frequency band, and the signal frequency that makes the voltage amplification factor drop to the multiple of the middle frequency band in the low frequency band is called the lower frequency FL

The signal frequency that lowers the voltage amplification factor to the multiple of the mid-band in the high frequency band is called the upper frequency fh pass band fbw

The frequency band that lies between the lower and upper frequencies, i.e., FBWFH FL

The frequency band of the multi-stage circuit is narrower than that of the single-stage power marketing network, and its lower limit frequency is higher than that of the single-stage circuit and the upper limit frequency is lower than that of the single-stage circuit.

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To change the answer you're looking for: The transistor is a commonly used electronic component that is often used in amplifiers, switching, and voltage regulation circuits. When amplifying an alternating current signal, the relationship between the frequency of the transistor and the amplified alternating current frequency is as follows:

The frequency of the transistor refers to the highest frequency that the transistor can amplify, which is usually expressed by the cut-off frequency fc. The cut-off frequency fc means that when the input signal frequency reaches a certain value, the output signal amplitude will drop by 3dB, that is, the output power will drop by 50%. The cut-off frequency of the transistor is related to the structure and working conditions of the transistor, generally between a few hundred kilohertz and several gigahertz.

Amplification alternating current frequency refers to the frequency of the input signal, in the amplification process of the transistor, the frequency of the input signal must be less than the cut-off frequency of the transistor, otherwise the transistor can not amplify the signal. When the input signal frequency is less than the cut-off frequency of the triode, the amplification of the transistor is inversely proportional to the frequency of the input signal, that is, the lower the frequency of the input signal, the higher the amplification of the triode. Therefore, the relationship between the frequency of the transistor and the frequency of amplified alternating current is that when the frequency of the input signal is less than the cut-off frequency of the transistor, the transistor can amplify the input signal, and the lower the frequency of the input signal, the higher the amplification of the transistor.

Dear, hello, I am glad to serve you, according to your question, there is a certain relationship between the frequency of the transistor and the frequency of amplified alternating current. The higher the frequency of the tripolar parallel elimination tube, the higher its amplified alternating current frequency. Therefore, the frequency of the transistor can be used to control the amplified AC frequency.

When the frequency of the transistor decreases, the amplified alternating current frequency also decreases; When the frequency of the transistor increases, the frequency of amplified intersecting bends also increases. In addition, the frequency of the transistor disturber can also be used to control the amplitude of the amplified alternating current, thereby changing the output power of the amplified alternating current.

The first feature is the fluidic feature. We call the current flowing between be the base current, and at the C pole (collector), the current between CE is called the current. That is to say, when there is an electric current, there is also an electric current;

There is no current, and there is no current. That is, the current that is controlled by the current.

The second feature, the transistor has an amplification function. For example, if the current flowing up is 1mA, then the current flowing through the mill is magnified by a large circle of the current that flows through the mill, and the magnification factor is 90 100 times, that is, = 100. This is determined by the characteristics of the transistor itself.

The third characteristic, when the e-pole is grounded, is larger if it is large enough, which indicates that the resistance between them is even smaller. Because the higher the current, the lower the resistance. It's so small that we approximate that the CE is short-circuited between them.

When is the current so large that we think the current between the CE is short-circuited? We generally think of it as 1 mA at the time. It is purely nonsense to say, when "=1ma, 0, .

The fourth trait, when >> = 1mA, =. At this time, we believe that the transistor is fully open. It just acts as a switch, =100mA, 0,,=.

The fifth characteristic is that in order for the transistor to be fully conducted, a voltage greater than that must be added to both ends of the transistor is fully conducted. If the voltage at both ends is less, then the transistor will not be fully conducted, and the current will not be maximum. This partial voltage value is equivalent to a resistor, and as it increases, it becomes smaller and smaller.

The most basic and important characteristics of the transistor: the transistor has the effect of current amplification, and its essence is that the transistor can control the large change of collector current with a small change in the base current.

The ratio of δic δib is called the current amplification of the transistor and is denoted by the symbol " ". The current amplification factor is a fixed value for a certain transistor, but it will also change to a certain extent as the triode works as the base current changes.

When the voltage applied to the transmitting junction of the triode is less than the on-voltage of the pn junction, the base current is zero, the collector current and the emitter current are zero, and the transistor loses its current amplification effect.