This circuit allows you to couple a TTL circuit output to the input of a CMOS circuit. The base is a quarter of a quadruple 339 voltage comparator (LM339, or equivalent) that is powered with a voltage of 5 V and -1 2V of symmetrical source. Note that the output signal has a transition from 0 to -12 V on this circuit. The 1.4 V reference voltage can be obtained from a resistive divider connected to the +5 V point or by diodes.
