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PNP Current Source Reference Circuit

IP.com Disclosure Number: IPCOM000061595D
Original Publication Date: 1986-Aug-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 39K

Publishing Venue

IBM

Related People

Houghton, RJ: AUTHOR

Abstract

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.

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PNP Current Source Reference Circuit

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. When these circuits are combined in a negative feedback configuration, the voltage at node 2 is very close to the reference voltage VR. If the base current of T2 is very small compared to the collector current of T4, the collector current of T4 will be approximately VR/R1. When a PNP current source (shown) is connected to the reference output VREF, where R5 = R5' and T4 = T4', then the value of load current (IL) is equal to VR/R1. Other values of load current are determined by the value of the current source resistor R5'. More than one current source may be attached to VREF, as shown by the fan-out symbol. The resulting additional load on the reference circuit is compensated by the fe...