a push - pull driver circuit operative with two input logic signals of opposite sense has a first bipolar transistor with a base terminal connected to a first input signal , and an emitter terminal connected to a second bipolar transistor which takes the place of the emitter resistor in the usual construction of an emitter follower circuit . during an activation of the first transistor to pass current , this being the pull - up stage , the second transistor is in a quiescent state to develop a voltage drop provided by current flow from the first transistor . a current mirror maintains a small quiescent current in the second transistor so that it can be activated rapidly upon occurrence of the pull - down transition . during a deactivation of the first transistor to terminate current flow in the first transistor , the voltage drop across the second transistor decreases , this being the pull - down stage . the voltage drop across the second transistor serves as an output signal of the driver circuit . during the pull down stage , the second transistor is activated momentarily via the capacitance of a back - biased transistor to pass current for rapid reduction of the voltage drop across the second transistor , this being in response to the second input signal . to avoid placing the second transistor in a state of saturation , a bypass transistor is connected across the base - collector terminal of the second transistor in the reverse direction of current flow in the second transistor to prevent the development of excessive base drive to the second transistor .