Schottky diode between base to emitter terminal


Joined Jun 19, 2012
It clamps the node there to negative ~0.4 volts on the negative edge of the input waveform.

This is called "DC restoration" the signal on the cathode then goes from ground to the highest input voltage- remaining positive.
It also prevents possible reverse breakdown of the BE junction if in input voltage is over 14V P-P.