| 摘要 |
PURPOSE:To make an output current variable by providing the method of generating a bias voltage for an output transistor at the drain of IGFET and the method of switching the gate of the output transistor between the bias voltage and the earth potential. CONSTITUTION:When the input terminal of I1 is held at a high level and the input terminals of I2 and I3 are both at a low level, insulating-gate fieled effect transistor IGFETE15 conducts and IGFETE16 becomes unconductive to hold the gate of IGFETE12 at the same potential as that at node 12, allowing IGFETE12 to conduct. At this time, IGFETE13 and E14 are unconductive being grounded at the gates, so that a reference current to flow FETE12 will flow to output terminal 6. Next, when I1 and I3 are at the low level and I2 is at the high level, FETE13 conducts and FETE12 and E14 become unconductive, so that a current twice the reference current will flow to terminal 6. Similarly, changing combinations of input levels of I1, I2 and I3 obtains combinations of output currents as many as 2<3> including when the output current is zero, so that the three-bit current output type D/A converter can be obtained. |
