# Transient current in transistor

Hi Juan:

I want to simulate the transient current in the transistor.

While the gate voltage was powered by the source meter, the gate current would be limited by the series resistance. So I used the following scripts to create the circuit.

contact_equation(device=device, contact=contact, name=“PotentialEquation”, variable_name = “Potential”, node_model=contact_model_name, edge_charge_model= “PotentialEdgeFlux”, circuit_node=GetContactBiasName(“gate”))

circuit_element(name=“V1”, n1=1, n2=0, value=0.0, acreal=acreal)
circuit_element(name=“R1”, n1=GetContactBiasName(“gate”), n2=1, value=resistance)

To solve the cuiuit:
devsim.solve(type=“transient_dc”, absolute_error=abs_error, relative_error=rel_error, maximum_iterations=iterations, tdelta=tdelta, charge_error=1e10)

The following to gate the current of source supply:
get_circuit_node_value(node=“V1.I”, solution=“dcop”)

The output current stays at 0.
Before I solve the transient current, I have set the gate bias to a constant like -60V.
is this cause the error? Hope you can give me some advice.

Best regards,
QS.C

Hi @QsChen

The `transient_dc` step is to store the initial condition, before the transient solve. The current through `V1.I` will be zero, since no time integration has been performed.

Please see the `testing/transient_circ.py` example showing s simple circuit with a step response. After the initial transient_dc solution, the `circuit_alter` command is used to step the voltage. Then a series of `transient_bdf` steps are used to get the step response to the change in voltage.

I recommend the `transient_bdf` method since it is the easiest time integration method to work with.

As you can see from these examples in the `testing` directory, there are no formal device simulation examples, and there is little documentation. Please let me know if you have additional questions.

Hi Juan:

The drain current didn’t vary with time. It stays in the off state. But as a p_type transistor, the drain current should increase with time after the negative gate bias was applied. The outputs are listed below. the gate bias reaches -60 in the beginning. So whether I should define the very contacts of the transistor in the circuit?

Circuit Solution:
1 -60
V1.I 2.93072e-35
gate_bias -60

Regards,

QS.C

A resistor limits how fast the current can flow into the gate. Remove the resistor and node 1 from your circuit, and attach the voltage source directly to the gate.

Adding the other contacts to the circuit is not necessary, as there is no charge at the ohmic contacts to integrate. Attaching the circuit to the gate is required to account for the capacitance.

-60 V is an abrupt change in voltage. You may want to ramp from 0 to -60 over several time steps.