This paper presents a novel logi-thermal simulator architecture. A logi-thermal simulator encorporates a logic and a thermal core in strong coupling. It is capable of calculating the self-heating of digital blocks and is able to account for the consequences of temperature change by implementing the delays of the blocks as a function of the temperature. The simulator architecture presented is able to work with logic entities described at different levels of abstraction. This allows to simulate a design at a very early phase when only high-level descriptions are available or to simulate systems that have elements in different design phases. Such a feature enables engineers to perform logi-thermal simulation throughout almost the entire design process which allows for the application of multiple-level optimization. It can also be used to shorten simulation times when only some parts of the design need to be simulated in high detail.