Electric current switch circuit and d/a converter using same

Abstract

An electric current switch circuit in accordance with the present invention is arranged so that an output of an IIL logic circuit is connected with the base of the first transistor of NPN type that switches ON or OFF the electric current. The first constant current source and the second transistor cause the first transistor to switch ON during a period when the output of the IIL logic circuit is in an OFF state, to switch OFF during a period when the output of the IIL logic circuit is in an ON state. Thus, only a voltage of 0.9V to 1.1V (the sum of a drop voltage across the first resistor and the base-emitter voltage) is applied to the base of the first transistor. Accordingly, a voltage less than the withstand voltage of the IIL logic circuit is applied to the base of the first transistor. This allows the electric current switch to be realized by three transistors and one resistor when the first current source is an NPN transistor and, therefore, in an electric current switch that switches ON or OFF the electric current in response to the output of the IIL logic circuit, it is possible to reduce the circuit scale and the power consumption and to lower the lower limit of the output voltage.