Tri-state type driver circuit

摘要

This invention relates to a tri-state type driver circuit in which any one of the three possible output signals of "float", "on", or "off" is produced at high speed even when an output terminal is accompanied with a great load. The tri-state type driver circuit comprises an output inverter circuit which employs a bipolar transistor as a load thereof and a MOS-FET as a driver thereof, a first logical circuit which is coupled to an input terminal of the bipolar transistor, which first logical circuit is made up of a C-MOS circuit receiving an external select signal and a C-MOS circuit having an input signal transmitted thereto and whose output can be specified by the external select signal, and a second logical circuit which is coupled to an input terminal of the MOS-FET, which second logical circuit is made up of a C-MOS circuit receiving the external select signal and a C-MOS circuit having the input signal transmitted thereto. The state of the external select signal will determine whether the driver circuit output will be "float" (regardless of the input to the driver circuit) or "on" or "off" (in correspondence with the input to the driver circuit).