Analysis of Voltage Divider Biasing using Graphical Method

4. Analysis of Voltage Divider Biasing using Graphical Method

• We know that, for voltage divider biasing

V_S = I_DR_S … (3.6.6)

and V_GS = V_G - I_DR_S … (3.6.7)

• These equations can be used with a transfer characteristics to find the Q point.

• Fig 3.6.18 shows a transfer characteristics for a voltage divider bias circuit.

• This point is located on the transfer characteristics as a point A.

• This point is located on the transfer characteristics as a point B.

• The straight line between points A and B represents equation (3.6.7).

• The intersection of this straight line with the transfer curve in the region to the left of the vertical axis is the operating point (Q point).

Ex. 3.6.11 Determine I_DQ, V_GSQ V_D, V_DS and V_DG for the circuit shown in Fig. 3.6.19 using graphical analysis.

Sol. :

Step 1 : Draw the transfer characteristics and determine I_DQ and V_GSQ.

We know that, 

• The curve representing these values obeys the Shockey’s equation in Fig. 3.6.20

Review Questions

1. Draw two different circuits that bias a JFET amplifier.

2. Draw the source self bias and voltage divider bias circuit for FET.

3. Explain the self bias circuit for n-channel FET and give its d.c. analysis.

4. With the help of a neat diagram explain the voltage divider biasing method for JFET.