Question 4.SP.16: Find the equivalent of the two identical n-channel JFETs con......

Assume the devices are described by (4.2); then
i_D = I_{DSS} \left( 1 + \frac{v_{GS}}{V_{p0}} \right)^2              (4.2)
i_D = i_{D1} + i_{D2} = I_{DSS} \left( 1 + \frac{v_{GS}}{V_{p0}} \right)^2 + I_{DSS} \left( 1 + \frac{v_{GS}}{V_{p0}} \right)^2 = 2I_{DSS} \left( 1 + \frac{v_{GS}}{V_{p0}} \right)^2

Because the two devices are identical and connected in parallel, the equivalent JFET has the same pinchoff voltage as the individual devices.    However, it has a value of shorted-gate current I_{DSS} equal to twice that of the individual devices.