Temperature-compensated low-voltage bandgap reference
View Patent ↗A low-voltage bandgap reference circuit includes a current source supplying a reference voltage rail. A first BJT has a collector coupled to the voltage rail via a resistor, a base coupled directly to the voltage rail, and an emitter coupled to ground via an emitter resistance. A second BJT has a collector coupled to the voltage rail via a resistor, a base coupled to voltage rail by a first base resistance and to ground via a second base resistance, and a collector coupled to the emitter resistance via an intermediate resistance. A third BJT has a collector driven by a current source, a base coupled to a node between the first and second base resistances, and an emitter coupled to ground. A feedback amplifier regulates the reference voltage rail to equalize collector voltages of the first and second BJTs.
1. A low-voltage bandgap reference circuit comprising:
a first current source (I 2 ) coupled to supply current to a reference voltage rail;
a first bipolar junction transistor (Q 1 ) having a collector coupled to the reference voltage rail via a first collector resistance (RC 2 ), a base coupled directly to the reference voltage rail, and an emitter coupled to a ground node via an emitter resistance (R 2 );
a second bipolar junction transistor (Q 0 ) having a collector coupled to the reference voltage rail via a second collector resistance (RC 1 ), a base coupled to the reference voltage rail by a first base resistance (R 4 ) and coupled to the ground node via a second base resistance (R 3 ), and an emitter coupled to the emitter resistance by an intermediate resistance (R 1 );
a third bipolar junction transistor (Q 2 ) having a collector driven by a second current source (I 1 ), a base coupled to a node between the first and second base resistances, and an emitter coupled to the ground node; and
a feedback amplifier (S) that regulates the reference voltage rail to equalize collector voltages of the first and second bipolar junction transistors.
2. The circuit of claim 1 , wherein the first bipolar junction transistor provides a first base emitter voltage (Vbe 1 ) having a negative temperature coefficient, wherein the second bipolar junction transistor provides a second base emitter voltage (Vbe 0 ) that yields a differential voltage (ΔVbe) when subtracted from the first base emitter voltage, the differential voltage having a positive temperature coefficient, and wherein the third bipolar junction transistor provides a third base emitter voltage (Vbe 2 ) to fractionally reduce the differential voltage.
3. The circuit of claim 2 , wherein the first and second collector resistances are equal, wherein a first ratio of the emitter resistance to the intermediate resistance (R 2 /R 1 ) and a second ratio of the first base resistance to the second base resistance (R 4 /R 3 ) balance contributions from the positive and negative temperature coefficients to ensure that the reference voltage rail is temperature compensated and maintained below 1.2 volts.
4. The circuit of claim 3 , wherein the first current source supplies said current from a voltage that does not exceed the reference voltage rail by more than 10 millivolts.
5. The circuit of claim 3 , wherein the second bipolar junction transistor has an emitter area N times larger than an emitter area of the first bipolar junction transistor.
6. The circuit of claim 5 , wherein the reference voltage rail has a regulated voltage of
Vref
=
2
R
2
R
1
kT
q
ln
N
+
V
be
1
-
2
V
be
2
R
4
R
3
R
2
R
1
.
7. The circuit of claim 3 , wherein to regulate the reference voltage rail, the feedback amplifier drives a gate voltage of a MOSFET coupled between the reference voltage rail and the ground node.
8. The circuit of claim 3 , further comprising an n-channel MOSFET having a drain coupled to the base of the second bipolar junction transistor, a gate coupled to the collector of the third bipolar junction transistor, and a source coupled to the base of the third bipolar junction transistor.
9. A method of providing a low-voltage bandgap reference, the method comprising:
driving a reference voltage rail with a current from a first current source (I 2 );
providing a first base emitter voltage (Vbe 1 ) with a first bipolar junction transistor (Q 1 ) having a collector coupled to the reference voltage rail via a first collector resistance (RC 2 ), a base coupled directly to the reference voltage rail, and an emitter coupled to a ground node via an emitter resistance (R 2 );
providing a second base emitter voltage (Vbe 0 ) with a second bipolar junction transistor (Q 0 ) having a collector coupled to the reference voltage rail via a second collector resistance (RC 1 ), a base coupled to the reference voltage rail by a first base resistance (R 4 ) and coupled to the ground node via a second base resistance (R 3 ), and an emitter coupled to the emitter resistance by an intermediate resistance (R 1 );
providing a third base emitter voltage (Vbe 2 ) with a third bipolar junction transistor (Q 2 ) having a collector driven by a second current source (I 1 ), a base coupled to a node between the first and second base resistances, and an emitter coupled to the ground node; and
regulating the reference voltage rail with a feedback amplifier (S) that operates to equalize collector voltages of the first and second bipolar junction transistors.
10. The method of claim 9 , wherein the first base emitter voltage has a negative temperature coefficient, wherein the intermediate resistance sustains a differential voltage (ΔVbe) between the first and second base emitter voltages, reduced by a fraction of the third base emitter voltage, the reduced differential voltage having a positive temperature coefficient.
11. The method of claim 10 , wherein the first and second collector resistances are equal, wherein a first ratio of the emitter resistance to the intermediate resistance (R 2 /R 1 ) and a second ratio of the first base resistance to the second base resistance (R 4 /R 3 ) balance contributions from the positive and negative temperature coefficients to ensure that the reference voltage rail is temperature compensated and maintained below 1.2 volts.
12. The method of claim 11 , wherein the first current source supplies said current from a voltage that does not exceed the reference voltage rail by more than 10 millivolts.
13. The method of claim 11 , wherein the second bipolar junction transistor has an emitter area N times larger than an emitter area of the first bipolar junction transistor.
14. The method of claim 13 , wherein the reference voltage rail has a regulated voltage of
Vref
=
2
R
2
R
1
kT
q
ln
N
+
V
be
1
-
2
V
be
2
R
4
R
3
R
2
R
1
.
15. The method of claim 11 , wherein to regulate the reference voltage rail, the feedback amplifier drives a gate voltage of a MOSFET coupled between the reference voltage rail and the ground node.
16. A method of providing a low-voltage bandgap reference, the method comprising:
manufacturing an integrated circuit having:
a first current source (I 2 ) coupled to supply current to a reference voltage rail;
a first bipolar junction transistor (Q 1 ) having a collector coupled to the reference voltage rail via a first collector resistance (RC 2 ), a base coupled directly to the reference voltage rail, and an emitter coupled to a ground node via an emitter resistance (R 2 );
a second bipolar junction transistor (Q 0 ) having a collector coupled to the reference voltage rail via a second collector resistance (RC 1 ), a base coupled to the reference voltage rail by a first base resistance (R 4 ) and coupled to the ground node via a second base resistance (R 3 ), and an emitter coupled to the emitter resistance by an intermediate resistance (R 1 );
a third bipolar junction transistor (Q 2 ) having a collector driven by a second current source (I 1 ), a base coupled to a node between the first and second base resistances, and an emitter coupled to the ground node; and
a feedback amplifier (S) that regulates the reference voltage rail to equalize collector voltages of the first and second bipolar junction transistors; and
packaging the integrated circuit.
17. The method of claim 16 , wherein the first bipolar junction transistor provides a first base emitter voltage (Vbe 1 ) having a negative temperature coefficient, wherein the second bipolar junction transistor provides a second base emitter voltage (Vbe 0 ) that yields a differential voltage (ΔVbe) when subtracted from the first base emitter voltage, the differential voltage having a positive temperature coefficient, and wherein the third bipolar junction transistor provides a third base emitter voltage (Vbe 2 ) to fractionally reduce the differential voltage.
18. The method of claim 17 , wherein the first and second collector resistances are equal, wherein a first ratio of the emitter resistance to the intermediate resistance (R 2 /R 1 ) and a second ratio of the first base resistance to the second base resistance (R 4 /R 3 ) balance contributions from the positive and negative temperature coefficients to ensure that the reference voltage rail is temperature compensated and maintained below 1.2 volts.
19. The method of claim 18 , wherein the second bipolar junction transistor has an emitter area N times larger than an emitter area of the first bipolar junction transistor, and wherein the reference voltage rail has a regulated voltage of
Vref
=
2
R
2
R
1
kT
q
ln
N
+
V
be
1
-
2
V
be
2
R
4
R
3
R
2
R
1
.
20. The method of claim 18 , wherein to regulate the reference voltage rail, the feedback amplifier drives a gate voltage of a MOSFET coupled between the reference voltage rail and the ground node.