4.2 Code structure

  SIMON consists of two main blocks, the   graphical user interface (GUI) written in tcl/tk [57] [94] and the circuit simulator written in ANSI-C [60]. The primary means of communication are ASCII files for the circuit description (*.set) and simulation results (*.set.i*, *.set.u*, *.set.q*). The circuit simulator additionally communicates error and status information to the GUI which informs the user about the simulation progress. The decision to use ASCII files as the interface between GUI and circuit simulator has two reasons. First we wanted to stay compatible with text only systems. SIMON can fully be used with a text terminal. Secondly, it nicely separates the two main parts and facilitates development. In addition the usual ASCII files involved are not very large. Fig. 4.1 shows the main building blocks of SIMON.

  

Figure 4.1: The main building blocks of SIMON.

 

SIMON is capable of simulating an arbitrary connection of tunnel junctions, capacitors, constant voltage sources, piece-wise linearly time dependent voltage sources, and voltage controlled voltage sources. No principal restrictions on the number of junctions or nodes exist. SIMON automatically detects missing connections of circuit objects and short circuits of voltage sources. Co-tunneling can be simulated up to any order desired. However, the run time of the simulation grows exponentially with the order of co-tunneling, which sets a practical limit.