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Chapter 16
Electrothermal Simulation
This chapter describes the electrothermal simulation available in Eldo.
Electrothermal Simulation Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 715
Specifying an Electrothermal Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 716
Verilog-A Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 720
Reporting and Sorting Thermal Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 723
Electrothermal Simulation Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 724
Electrothermal Simulation Overview
Eldo supports fully coupled electrothermal simulation. In high voltage/power applications, the
control of the temperature and its propagation throughout the circuit and the system become
critical. Using a global uniform temperature for the entire IC is no longer accurate enough.
Devices consuming power tend to heat, and this heat propagates to the devices in the vicinity,
through thermal coupling. The temperature at which a device operates (for example a simple
resistor, a DMOS, or bipolar device) modifies its electrical characteristics. Some particular
characteristics might have exponential dependencies with the temperature, such as leakage
currents.
As the electrical characteristics change, so does the dissipated power, and thus the heat, and so
on. Everything (the electrical performance and the temperature) becomes tightly coupled and
interacting, and cannot be calculated in isolation. The electrical and thermal equations must
truly belong to the same system for accurate resolution.
Eldo solves this problem by allowing the local temperature of devices or entire cells
(subcircuits, in SPICE terminology) to be true variables of the system. Temperatures are solved
simultaneously with the voltages and the currents through the devices. This is called true
electrothermal simulation.
This flow requires the inclusion of an estimated thermal network in the simulation netlist. This
network is typically composed of thermal resistors and capacitors. The thermal network
depends on the layout (the physical distance between the heating devices) and on the materials
used in the process.
Figure 16-1 shows the electrothermal simulation flow in Eldo.
Eldo® User's Manual, 15.3 715