- #1

Mr_Allod

- 42

- 16

- Homework Statement
- How fast will a PN JFET operate in GHz if the gate impedance is ##50\omega##, and if the JFET

has a drain-source voltage ##V_{DS} = 2V##

- Relevant Equations
- Capacitance: ##C = \frac {\epsilon A}{h}##

##\epsilon_r = 11.7##

N-channel thickness ##T = 125nm##

N-channel width ##W = 75\mu m##

N-channel length ##L = 0.8\mu m##

##N_D = 4\times 10^{18} cm^{-3}##

##N_A = 2\times 10^{17} cm^{-3}##

Hello there, I believe here I need to find the capacitance of the junction between the P-doped gate and N-channel. Then I could find the RC time constant although I am not sure if there's something more I need to find the speed of the JFET?

What I'm unsure of is the depletion width h to use for the calculation. Since I am given a drain-source voltage ##V_{DS}## I think I am dealing with an uneven depletion layer, ie. the depletion layer is larger near the drain than it is near the source. I know how to calculate the width h at each point using the abrupt junction approximation but then I don't know what to actually use for the capacitance. Do I need to integrate in some way to account for the varying depletion width?

I'd appreciate some help with this.

What I'm unsure of is the depletion width h to use for the calculation. Since I am given a drain-source voltage ##V_{DS}## I think I am dealing with an uneven depletion layer, ie. the depletion layer is larger near the drain than it is near the source. I know how to calculate the width h at each point using the abrupt junction approximation but then I don't know what to actually use for the capacitance. Do I need to integrate in some way to account for the varying depletion width?

I'd appreciate some help with this.