| 摘要 |
A low voltage CTAT current source includes a bipolar transistor connected across two series-connected resistors. A voltage developed across the resistors turns on the transistor, making the current through the resistors CTAT. A second transistor supplies the resistor current; its base (if bipolar) is connected to the node between the resistors, which are selected to limit the transistor's base-collector forward bias and collector-emitter voltage to a preselected fraction of the first transistor's Vbe, allowing the CTAT current source to operate with supply voltages of less than two junction voltage drops. A PTAT current can be combined with the CTAT current to create a temperature-compensated current. A low voltage current mirror has the respective bases of a pair of cascoded transistors connected across a resistor which is also connected between the bottom transistor's collector and a programming current. When the transistors are matched, the top transistor's collector-emitter voltage about equals the voltage across the resistor, which is selected to establish a Vce just high enough to avoid saturation and allow the circuit to operate with only two unsaturating Vce's of headroom. The current mirror's lower headroom requirements are advantageously employed in a low voltage differential to single-ended converter circuit, and the current mirror and CTAT current source can be combined in numerous analog circuits to enable their operation at lower supply voltages. |
