In this particular post, you will be learning three different biasing techniques and at the end, I had inserted one video which explains the working of JFET as an amplifier, and at the same time, it will show you that how the output of JFET is 180 degree out of phase with respect to the input.
So in total, there are 3 biasing techniques of JFET and they are as follows
1) Fixed biasing technique
2) Self-biasing technique and
3) Voltage-divider biasing
You will get to know the working of each biasing technique in great depth but before that please subscribe to my site by clicking on that bell icon. So let's start with the working of each biasing technique of JFET.
1) Fixed biasing technique of JFET:-
As we saw in the previous post that the gate voltage is kept negative so in this technique we are keeping the gate voltage at the fixed point. As we had seen in the previous post that the input impedance of the JFET is very high(theoretically input impedance is infinite and practically in MΩ) therefore the current through resistor R1 will be zero I=0mA thus we can say that the voltage drop across the resistor R1 is 0v that is VR1=0v.
2) Self-biasing technique of JFET:-
When we add or basically when we connect the source resistance to a fixed bias circuit then the circuit is known as the self-biasing circuit. Now you will be thinking that why this circuit is known as a self-bias circuit to understand it just look at the figure given below. When we apply KVL to the gate loop we get equation (1) as shown in the figure.
Vgs = -Id*Rs
3) Voltage-Divider Biasing technique of JFET:-
Voltage divider biasing is also known as potential-divider biasing. In this technique, an additional resistor is connected between the supply voltage and gate resistor. The additional gate resistor Rl from gate to supply voltage facilitates the larger adjustment of the dc bias point. Also, remember one thing that while designing the amplifier with this circuit the source voltage must be greater than the voltage across R2 so that the Vg will always be negative. Thus by using this technique, we are able to change the Vgs according to our will, and thus by using this single circuit we can actually use it for different applications such as a switch or as an amplifier.
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