The transient simulation of vpd



dear supporter,
In the example of vpd_transient.ldev, I want to know this simulation only consider the transit time of carrier? For the resistance and capacitance of the vpd, it will not reflect in the transient simulation, because when I change the width of the vpd, it will not change for 3dB bandwidth.

The simulation result of 3dB in 2D including the device of RC?

Hi @mapengcheng,

This point has been discussed in an older topic that you created yourself in the following link (see the last post):


I think the bandwidth has not any change as increasing the length, because the simulation based on 2D, which doesn’t consider the factor of length. But for width, it can see in 2D simulation. Even if the transit time is the dominant limiting factor for bandwidth, when I changed the width, the resistance will increase, the bandwidth will change a little in fact, but in this simulation, it doesn’t any change. Then I add 50ohm at anode ( equal to increase the width), the bandwidth dropped.


The length of a device in 2D simulation can be adjusted using the “norm length” parameter in CHARGE settings.

This device’s bandwidth is mostly limited by carrier transit time unless the capacitance and/or resistance of the device become so large that the RC-limited bandwidth (1/2piRC) becomes dominant. So when you have a drop in bandwidth as a results adding a resistor, it means the bandwidth is now limited by RC.


dear supporter,
In 2D simulation, the 3dB of VPD in example including the RC influence or only the transient influence. I am very confused the device of RC how to show in 2D simulation?


I didn’t quite understand your question. Can you provide more details about what the issue in 2D simulation is, and share your simulation and any results that you have so we can better understand the problem.