INTERFACE CIRCUIT

摘要

PURPOSE:To improve the working reliability of an interface circuit by keeping the circuit threshold value at a fixed level regardless of the fluctuation of the base-emitter voltage of a bipolar transistor TR. CONSTITUTION:The npn TR Q11 and Q12 are equally affected by the fluctuation of the manufacturing conditions. Thus the base-emitter voltage of the TR Q11 rises up with the rise of the base-emitter voltage of the TR Q12. In the same way, the base-emitter voltage of the TR Q11 drops with the drop of the base- emitter voltage of the TR Q12. The potential of a node N11 is dependent on the base-emitter voltage level of the TR Q11. Thus the potential of the node N11 rises up with the rise of the base-emitter voltage of the TR Q12 and vice versa. Thus it is possible to keep the threshold voltage at a fixed level regardless of the fluctuation of the base-emitter voltage ae long as the potential of the node N11 is corrected against the fluctuation of the base-emitter voltage of the TR Q12. As a result, the working reliability is improved for an interface circuit.