A JFET is similar to a MOSFET, but different in a couple regards. The most immediate difference is that a JFET is a depletion-mode device, as opposed to MOSFETs which are typically (but not always) enhancement-mode devices. Enhancement-mode devices are insulating by default, and begin to conduct when a voltage is applied to the gate. A depletion-mode device is conducting by default and only insulates when the opposite voltage is applied to a gate. For N-type devices, a positive voltage is required to turn on an enhancement-mode device, and a negative voltage is required to turn off a depletion-mode device. For P-type, the voltages are reversed, much like the relationship between NPN and PNP BJTs. In order to model this behavior, I have added a 1V voltage source to give a negative effective VTO instead of the usual positive VTO for EC MOSFETs. By having a negative VTO, it becomes a depletion-mode device.
The other main difference is that the gate is not insulated from the source/drain and may conduct depending on the voltage applied. This behavior is modeled by the two diodes.
Another interesting difference is that while a MOSFET is asymmetric due to the body diode, a JFET is more or less symmetric and the source and drain can often be used interchangeably. Fortunately, EC simulates MOSFETs symmetrically, so that behavior is automatically present in this model.
