Contents
Why the voltage gain decreases as we move from mid frequency to low frequency?
The capacitive reactance of coupling and by pass capacitors is large at low frequencies. As this reactance with is in series with source resistance, the input signal is attenuated and the gain is less.
Why does high frequency decrease voltage gain?
At higher frequencies, the internal junction capacitors of transistor come into play, thus reducing the output and therefore the gain of amplifier. The capacitor reactance decreases with increase in frequency bypassing the majority of output. In some cases the output gets fed back to input as negative feedback.
Why the voltage gain gets reduced at the low frequency and high frequency regions?
The reduction of gain in the low frequency band is due to the coupling and bypass capacitors selected. They are essentially short circuits in the mid and high bands. The reduction of gain in the high frequency band is due to the internal capacitance of the amplifying device, e.g., BJT, FET, etc..
What is the effect of frequency change on voltage gain?
As the frequency increases, the capacitive reactance becomes smaller. This cause the signal voltage at the base to decrease, so the amplifier’s voltage gain decreases.
How is voltage gain of a transistor amplifier affected?
No matter if you use a low power transistor such as the 2N2222A or test with a large TO-220, you will find +0.7 volt on the base when the emitter is 0.0 volt (for NPN). The gain of transistor in datasheets is always given as a ratio of the input/output current. The input current flow from the base to the emitter.
How can a variable gain amplifier be used?
This can be done simply by using a potentiometer on the output of a fixed gain op-amp circuit, but sometimes it may be more useful to vary the actual gain of the amplifier circuit itself. A variable-gain or voltage-controlled amplifier is an electronic amplifier that varies its gain depending on a control voltage.
Why is the frequency of a tipical amplifier lower?
Depends of the schematic, for just a transistor it lowers with frequency, but in tipical amplifier it is c). At lower frequencies if coupled with capacitor gain is low because of reactance of that capacitor. At high frequencies it is lower because of transistor gain. If it is DC coupled, than have low gain only on high frequencies.
Is the current gain of a bipolar transistor constant?
It is normally expected that the value of current gain β for a bipolar transistor is constant, however there are some variations that occur in the value of β or h FE. β variations with collector current: The collector current level can cause a variation in the level of β or or h FE.