@User If you specifically refer to mixed signal as a circuit with analog components and digital components (using the XSPICE primitives) there is a small example in the xschem alone distribution, so start xschem outside of any directory with open_pdks xschemrc file, and load '`logic/test_ngspice.sch`' This example will simulate some logic gates at digital event level, then there are D/A and A/D converters to exit/enter the digital domain and pass node values to the ngspice analog engine.