Tri-state type driver circuit

Claim 1

A tri-state type driver circuit capable of providing "on" and "off" state outputs in response to the state of a driver circuit input signal applied to the driver circuit and a "float" state output which remains constant regardless of the state of said driver circuit input signal, comprising: an output inverter circuit to provide said three state outputs, which output inverter circuit employs a bipolar transistor as a load thereof and a MOS-FET as a driver thereof, a first logical circuit which is coupled with an input terminal of said bipolar transistor of said output inverter circuit, which first logical circuit is made up of a C-MOS circuit receiving an external select signal and a C-MOS circuit having the driver circuit input signal transmitted thereto, wherein the output of said first logical circuit can be specified by said external select signal, a second logical circuit which is coupled with an input terminal of said MOS-FET of said output inverter circuit, which second logical circuit is made up of a C-MOS circuit receiving said external select signal and a C-MOS circuit having the driver circuit input signal transmitted thereto, wherein the output of said second logical circuit can be specified by said external select signal, and a first C-MOS inverter which is coupled with said second logical circuit and which functions to invert said driver circuit input signal which is applied to said second logical circuit, wherein when the external select signal is in a first state, the first and second logical circuits will produce output signals to set the output of the output inverter circuit to the "float" state output, and when the external select signal is in a second state, the first and second logical circuits will produce output signals to allow the output of the output inverter circuit to be in the "on" or "off" state depending upon the state of the driver input signal.