PNP Current Source Reference Circuit
Original Publication Date: 1986-Aug-01
Included in the Prior Art Database: 2005-Mar-09
Sensing collector load current of a bipolar PNP current source transistor with a reference circuit improves the accuracy of the load current source. Lateral PNP transistors are known to have low gain and frequency response. When a lateral PNP transistor is used as a current source, the base current loading on a reference circuit is large and has a poor tolerance, which makes accurate control of the load current difficult. The PNP current source reference circuit shown in the figure achieves better control of the load current (IL). Transistors T3 and T4 in conjunction with resistors R4 and R5 form a current amplifier with node 1 as the input and the collector of T4 as the output. Transistors T1 and T2 and resistor R3 form a differential amplifier.