Harmonic balance simulation of RF injection effects in analog circuits

RF noise immunity is becoming a serious problem for integrated circuits (ICs). We have found a frequency-domain simulator [harmonic balance (HB)] to be useful for analyzing the undesired IC behavior, especially the DC output shift under the large RF injection. The simulator has the following advantages in comparison with a conventional time-domain simulator such as SPICE: (1) DC output shifts can be simulated in a very short time using a conventional bipolar transistor model and (2) steady-state current or voltage waveforms at each node in an IC are directly and easily obtained. This paper describes the methods and results of the DC shifts analysis of a bipolar transistor or a differential amplifier using the HB simulator.