2.4 Field effect transistor

The N-channel FET circuit shown in Figure 2.4 uses self-bias. Determine the voltage drop across the FET using a pinchoff voltage, V _p, of ? 5 volts and a saturation current, I _DSS, of 2 ma. Assume that the quiescent drain current, I _DS, equals 1 ma.

Figure 2.4: Field effect transistor

Solution:

I _DS = I _DSS (1 ? V _GS/V _P) ²

V _GS = V _P [1 ? (I _DS/I _DSS) ]

V _GS = ?5[1 ? (1/2) ] = ? 1.46 volts

V _DS = V _DD ? V _D ? V _S = 20 ? I _DS (R _D + R _S)

V _DS = 20 ? 1 10 ^?3(11.46 10 ³) = 20 ? 11.46 = 8.54 volts