I am using ultrasim to simulate the circuits. I always get the DC convergence error while simulating and the ultrasim simulation fails. This happens even for simple basic gates and also for other large circuits. Please help me to overcome this error. Looking forward to hearing from you soon.
Never tried UltraSim but it is an analog simulator. I have used HSPICE and HSIM though and they usually give convergence problems on digital blocks when there is a floating gate but perhaps a floating VDD/VSS might do it as well.
Make sure you defined in your test supplies for all globals and also every gate has something driving it.