Chapter 4
Q. 4.1
For the n-channel JFET in Figure 4–8, V_{GS(off)} = –4 V and I_{DSS} = 12 mA. Determine the minimum value of V_{DD} required to put the device in the constant- current region of operation.

Step-by-Step
Verified Solution
Since V_{GS(off)} = –4 V, VP = 4 V. The minimum value of V_{DS} or the JFET to be in its constant-current region is
V_{DS} = V_{P} = 4 V
In the constant-current region with V_{GS} = 0 V,
I_{D} = I_{DSS} = 12 mA
The drop across the drain resistor is
V_{R_{D} } = (12 mA) (560 \Omega ) = 6.7 V
Applying Kirchhoff’s law around the drain circuit gives
V_{DD} = V_{DS} + V_{R_{D} } = 4 V + 6.7 V = 10.7 V
This is the minimum value of V_{DD} to make V_{DS}= V_{P} and to put the device in the constant-current region.