Band-gap reference current source with compensation for saturation current spread of bipolar transistors

摘要

A reference current source for generating a reference current (Irf) includes a bipolar first transistor (2) and a bipolar second transistor (4), the base of the first transistor (2) being coupled to the base of the second transistor (4), a first resistor (6) connected between the emitter of the first transistor (2) and the emitter of the second transistor (4), and a second resistor (8) connected between the emitter of the second transistor (4) and a supply terminal (10). The current source also includes a measurement circuit (16) having inputs (12, 14) coupled to the collector of the first transistor (2) and the collector of the second transistor (4), and having a measurement output (18) for supplying a measurement signal in response to a difference in the collector current of the first transistor (2) and the second transistor (4), a bipolar third transistor (28) having its base coupled to the measurement output (18), having its emitter coupled to the bases of the first (2) and the second transistor, and having a collector supplying the reference current (Irf), and a bipolar fourth transistor (34) having its base coupled to the base of the third transistor (28), and having its emitter connected to the emitter of the third transistor (28) via a base pinch resistor (36). The base pinch resistor (36) provides compensation for variations in the reference current (Irf) caused by spread in the saturation current of the bipolar transistors.