Added resistance calculation

tests/test_components/test_heat_charge.py

@@ -711,6 +711,9 @@ def test_heat_charge_bcs_validation(boundary_conditions):
     with pytest.raises(pd.ValidationError):
         td.CurrentBC(source=td.DCCurrentSource(current=td.inf))
 
+    with pytest.raises(pd.ValidationError):
+        td.VoltageBC(source=td.DCVoltageSource(voltage=np.array([td.inf, 0, 1])))
+
 
 def test_heat_charge_monitors_validation(monitors):
     """Checks for no name and negative size in monitors."""
@@ -790,6 +793,7 @@ def test_device_characteristics():
         steady_dc_hole_capacitance=capacitance,
         steady_dc_electron_capacitance=capacitance,
         steady_dc_current_voltage=current_voltage,
+        steady_dc_resistance_voltage=current_voltage,
     )
 
 

tidy3d/components/spice/sources/dc.py

@@ -19,12 +19,14 @@
 
 """
 
-from typing import Optional, Union
+from typing import Optional
 
 import pydantic.v1 as pd
 
 from tidy3d.components.base import Tidy3dBaseModel
+from tidy3d.components.types import ArrayFloat1D
 from tidy3d.constants import AMP, VOLT
+from tidy3d.constants import inf as td_inf
 
 
 class DCVoltageSource(Tidy3dBaseModel):
@@ -45,11 +47,19 @@ class DCVoltageSource(Tidy3dBaseModel):
     """
 
     name: Optional[str]
-    voltage: Union[pd.FiniteFloat, list[pd.FiniteFloat]] = pd.Field(
+    voltage: ArrayFloat1D = pd.Field(
+        ...,
         title="Voltage",
         description="DC voltage usually used as source in 'VoltageBC' boundary conditions.",
+        units=VOLT,
     )
-    units: str = VOLT
+
+    @pd.validator("voltage")
+    def check_voltage(cls, val):
+        for v in val:
+            if v == td_inf:
+                raise ValueError(f"Voltages must be finite. Currently  voltage={val}.")
+        return val
 
 
 class DCCurrentSource(Tidy3dBaseModel):

tidy3d/components/tcad/data/sim_data.py

@@ -73,6 +73,14 @@ class DeviceCharacteristics(Tidy3dBaseModel):
         description="Device steady DC current-voltage relation for the device.",
     )
 
+    steady_dc_resistance_voltage: Optional[SteadyVoltageDataArray] = pd.Field(
+        None,
+        title="Small signal resistance",
+        description="Steady DC computation of the small signal resistance. This is computed "
+        "as the derivative of the current-voltage relation, delta(V)/delta(I) and the result "
+        "is given in Ohms. Note that in 2D the resistance is given in :math:`\\Omega \\mu`.",
+    )
+
 
 class HeatChargeSimulationData(AbstractSimulationData):
     """Stores results of a :class:`HeatChargeSimulation`.

tidy3d/components/tcad/simulation/heat_charge.py

@@ -434,11 +434,8 @@ def check_voltage_array_if_capacitance(cls, values):
             for bc in bounday_spec:
                 if isinstance(bc.condition, VoltageBC):
                     if isinstance(bc.condition.source, DCVoltageSource):
-                        if isinstance(bc.condition.source.voltage, list) or isinstance(
-                            bc.condition.source.voltage, tuple
-                        ):
-                            if len(bc.condition.source.voltage) > 1:
-                                voltage_array_present = True
+                        if len(bc.condition.source.voltage) > 1:
+                            voltage_array_present = True
         if is_capacitance_mnt and not voltage_array_present:
             raise SetupError(
                 "Monitors of type 'SteadyCapacitanceMonitor' have been defined but no array of voltages "
@@ -521,15 +518,14 @@ def check_only_one_voltage_array_provided(cls, val, values):
                 if isinstance(bc.condition.source, DCVoltageSource):
                     voltages = bc.condition.source.voltage
 
-                if isinstance(voltages, tuple):
-                    if len(voltages) > 1:
-                        if not array_already_provided:
-                            array_already_provided = True
-                        else:
-                            raise SetupError(
-                                "More than one voltage array has been provided. "
-                                "Currently voltage arrays are supported only for one of the BCs."
-                            )
+                if len(voltages) > 1:
+                    if not array_already_provided:
+                        array_already_provided = True
+                    else:
+                        raise SetupError(
+                            "More than one voltage array has been provided. "
+                            "Currently voltage arrays are supported only for one of the BCs."
+                        )
         return val
 
     @pd.root_validator(skip_on_failure=True)