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Line Voltage Rejection in a Bandgap Voltage Reference

IP.com Disclosure Number: IPCOM000039960D
Original Publication Date: 1987-Sep-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 2 page(s) / 37K

Publishing Venue

IBM

Related People

Riggio, SR: AUTHOR

Abstract

A technique is described whereby an electrical circuit consisting of two transistors is added to a bandgap reference voltage generator (U.S. Patent 4,396,883) so as to provide output voltage stability in the event that the input voltage changes. The two-transistor circuit 10, as shown dotted in the figure, is added to the bandgap reference generator circuit to provide the stability required. Since transistors Q1 and Q2 represent the heart of the bandgap reference voltage generator, the accuracy of the voltage node (Vbg) depends on the ability of the other components in the circuit to hold the operating point of Q1 and Q2 as stable as possible. The stability of (Vbg) will cause an inaccurate output voltage (Vout). The collector voltage of Q1 and Q2 will cause changes in the value of Beta, known as "early effect".

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Line Voltage Rejection in a Bandgap Voltage Reference

A technique is described whereby an electrical circuit consisting of two transistors is added to a bandgap reference voltage generator (U.S. Patent 4,396,883) so as to provide output voltage stability in the event that the input voltage changes. The two-transistor circuit 10, as shown dotted in the figure, is added to the bandgap reference generator circuit to provide the stability required. Since transistors Q1 and Q2 represent the heart of the bandgap reference voltage generator, the accuracy of the voltage node (Vbg) depends on the ability of the other components in the circuit to hold the operating point of Q1 and Q2 as stable as possible. The stability of (Vbg) will cause an inaccurate output voltage (Vout). The collector voltage of Q1 and Q2 will cause changes in the value of Beta, known as "early effect". By inserting the two transistor circuit 10, consisting of transistors Q6 and Q7, the "early effect" subsequently produces a more accurate bandgap reference generator. Since Q6 and Q7 are emitter followers, the collector voltages of Q1 and Q2 are equal to one diode drop less than the reference voltage (Vout). Also, since the output voltage (Vbg) is very accurate, a feedback loop is created, insuring that the collector voltages of Q1 and Q2 produce stability and accuracy, through the addition of circuit 10. Without circuit 10, the collector voltages of Q1 and Q2 would fluctuate with the value of the rect...