Simulation studies on the transient dose rate effect of analog delay locked loops

This paper presents the transient dose rate (TDR) effect of analog Delay Locked Loops (DLLs). The analog DLL circuits are built upon a previous design, and the typical photocurrents are calculated by the Sentaurus TCAD. Both single double-exponential and dual double-exponential functions are successfully introduced to fit the different photocurrent waveforms with change of the simulated nodes, which then are integrated into the SPICE models for later circuit simulations. Firstly, the radiation effect of individual sub-circuits (e.g. charge pump) and their coupling relationships are analyzed. The simulation results show that the current-charge pump as the most sensitive module can result in the biggest clock error, followed by the voltage-controlled delay line; although the global radiation effect of DLL (use current-charge pump) is almost the same with the individual current-charge pump exposed to the radiation, there are still some coupled relationships exhibiting among modules. Also, the simulation results are qualitatively consistent with previous experiment phenomena; further, it is demonstrated that the voltage-charge pump technique can be used effectively to improve the TDR effect of the charge pump; lastly, the effect of global photocurrents on the rail span collapse is indirectly considered through power analysis. However, it is found that this effect can be negligible due to the very small variation of power.