| 摘要 |
There is described a BiCMOS switch circuit which allows a low voltage CMOS signal to control a bipolar current source or sink circuit. The circuit includes a current mirror circuit, drawing a constant current through a first bipolar transistor. The collector of that transistor is connected firstly through a second bipolar transistor to a circuit output, and secondly through a CMOS transistor to a positive voltage supply. Depending on an input control signal supplied to the gate of the CMOS transistor, that device can be switched on or off. When the CMOS transistor is switched off, the constant current through the first bipolar transistor is drawn through the circuit output. When the CMOS transistor is switched on, the constant current through the first bipolar transistor is drawn through the CMOS transistor, and the output current is zero. A digital-to-analog converter can be formed by making a group of such circuits, with half of each current mirror circuit in common, the circuits having different constant currents, and receiving different bits of an input digital signal at their respective control inputs. |
