You might not be familiar with how a FET works ... there are N-FETs and P-FETs. N-FETs are like NPN transistors – the gate pin needs to have higher voltage than the source pin for the FET ...

Notice that the function of the gate is the programmable part of the programmable junction transistor ... a good sawtooth (but do not load it much as it is at a high impedance). Also, the current out ...