Low noise voltage reference circuit

• US 20080224759A1
• Filed: 03/13/2007
• Published: 09/18/2008
• Est. Priority Date: 03/13/2007
• Status: Active Grant

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Marinca, Stefan
• Granted Patent: US 7,714,563 B2
• Time in Patent Office: Days
• US Class Current: 327/539
• CPC Class Codes: G05F 3/30 Regulators using the difference between the base-emitter voltages of two bipolar transistors operating at different current densities G05F3/26 takes precedence

Abstract

A low noise voltage reference circuit is described. The reference circuit utilizes a bandgap reference component and may include at least one of a current shunt or filter to reduce high and low noise contributions to the output. Further modifications may include a curvature correction component.

Claims

1. A bandgap reference circuit including an amplifier having an inverting and a non-inverting input and providing at its output a voltage reference, the circuit including:

a. a first pair of transistors coupled to the non-inverting input of the amplifier, the first pair including a first and second transistor of the circuit, the bases of the first and second transistor being commonly coupled, the first transistor being additionally coupled to the amplifier output via a feedback resistor, the second transistor being provided in a diode configuration,

b. a second pair of transistors, the second pair including a third and fourth transistor of the circuit, the third transistor being coupled to the inverting input of the amplifier, the emitters of the third and fourth transistors being coupled to ground via a reference resistor, the fourth transistor being provided in a diode configuration and being coupled via a coupling resistor to the second transistor, and

wherein the base of the third transistor is coupled to the commonly coupled first and second transistors, the collector of the third transistor being coupled to the collector of the first transistor such that the first and third transistors form a preamplifier to the amplifier, and further wherein the emitter areas of the first and fourth transistors are scaled to be larger than that the emitter areas of the second and third transistors such that two base-emitter voltage differences, of the form of proportional to absolute temperature (PTAT) voltages, are developed across the coupling and feedback resistors respectively, the resultant PTAT currents generating a PTAT voltage across the reference resistor, this PTAT voltage in combination with the base emitter voltages of the combined first second and third transistors being reflected at the output of the amplifier as a first order temperature insensitive voltage, and further wherein the circuit includes a filter provided between the non-inverting input and ground to minimize high band noise contributions to this temperature insensitive voltage.

2. The circuit as claimed in claim 1 further including a current shunt provided to shunt at least a portion of the feedback current away from the first transistor so as effect a reduction in the collector and base currents of the first and third transistors thereby reducing low band noise contributions to this temperature insensitive voltage.

3. The circuit as claimed in claim 2 wherein the current shunt is configured to reduce the collector current of the first and third transistors and as a result to effect a reduction in the base currents of the first and third transistors.

4. The circuit as claimed in claim 3 wherein the current shunt includes two npn transistors and one pnp transistor, the pnp transistor forming a fifth transistor of the circuit, the two npn transistors forming sixth and seventh transistors of the circuit.

5. The circuit of claim 4 wherein the emitter areas of the transistors are chosen such that the second and third transistors have a first emitter area, n, the fourth transistor has a second emitter area n1, the first transistor has a third emitter area, n2, the fifth transistor has a fourth emitter area, n3, the sixth transistor has a fifth emitter area, n4 and the seventh transistor has a sixth emitter area, n5, the emitter areas being scaled such that n5>

n4>

n3>

n2>

n1>

n.

6. The circuit of claim 1 wherein the filter includes a capacitor.

7. The circuit of claim 6 wherein the capacitor has a value less than 1000 pF.

8. The circuit of claim 7 wherein the capacitor has a value less than 200 pF.

10. The circuit of claim 1 further including a curvature correction component.

11. The circuit of claim 10 wherein the curvature correction component is configured to provide a correction voltage of the type TlogT of opposite sign to that of the first order voltage reference voltage output, the correction voltage being combined with the first order voltage reference to provide a curvature corrected voltage reference.

9. The circuit of claim 9 wherein the capacitor has a value of about 100 pF.

12. A bandgap reference circuit including an amplifier having an inverting and a non-inverting input and providing at its output a voltage reference, the circuit including:

a. a first pair of transistors coupled to the non-inverting input of the amplifier, the first pair including a first and second transistor of the circuit, the bases of the first and second transistor being commonly coupled, the first transistor being additionally coupled to the amplifier output via a feedback resistor, the second transistor being provided in a diode configuration,

b. a second pair of transistors, the second pair including a third and fourth transistor of the circuit, the third transistor being coupled to the inverting input of the amplifier, the emitters of the third and fourth transistors being coupled to ground via a reference resistor, the fourth transistor being provided in a diode configuration and being coupled via a coupling resistor to the second transistor, and

wherein the base of the third transistor is coupled to the commonly coupled first and second transistors, the collector of the third transistor being coupled to the collector of the first transistor such that the first and third transistors form a preamplifier to the amplifier, and further wherein the emitter areas of the first and fourth transistors are scaled to be larger than that the emitter areas of the second and third transistors such that two base-emitter voltage differences, of the form of proportional to absolute temperature (PTAT) voltages, are developed across the coupling and feedback resistors respectively, the resultant PTAT currents generating a PTAT voltage across the reference resistor, this PTAT voltage in combination with the base emitter voltages of the combined second and third transistors being reflected at the output of the amplifier as a first order temperature insensitive voltage, and further wherein the circuit includes a current shunt configured to shunt at least a portion of the feedback current away from the first transistor so as effect a reduction in the collector and base currents of the first and third transistors thereby reducing low band noise contributions to this temperature insensitive voltage.

13. The circuit as claimed in claim 12 wherein the current shunt is configured to reduce the collector current of the first and third transistors and as a result to effect a reduction in the base currents of the first and third transistors.

14. The circuit as claimed in claim 13 wherein the current shunt includes two npn transistors and one pnp transistor, the pnp transistor forming a fifth transistor of the circuit, the two npn transistors forming sixth and seventh transistors of the circuit.

15. The circuit of claim 14 wherein the emitter areas of the transistors are chosen such that the second and third transistors have a first emitter area, n, the fourth transistor has a second emitter area n1, the first transistor has a third emitter area, n2, the fifth transistor has a fourth emitter area, n3, the sixth transistor has a fifth emitter area, n4 and the seventh transistor has a sixth emitter area, n5, the emitter areas being scaled such that n5>

n4>

n3>

n2>

n1>

n.

16. The circuit of claim 12 further including a filter provided between the non-inverting input and ground to minimize high band noise contributions to this temperature insensitive voltage.

17. The circuit of claim 16 wherein the filter includes a capacitor.

18. The circuit of claim 17 wherein the capacitor has a value less than 1000 pF.

19. The circuit of claim 17 wherein the capacitor has a value less than 200 pF.

20. The circuit of claim 19 wherein the capacitor has a value of about 100 pF.

21. The circuit of claim 12 further including a curvature correction component.

22. The circuit of claim 21 wherein the curvature correction component is configured to provide a correction voltage of the type TlogT of opposite sign to that of the first order voltage reference voltage output, the correction voltage being combined with the first order voltage reference to provide a curvature corrected voltage reference.

23. A bandgap reference circuit including an amplifier having an inverting and a non-inverting input and providing at its output a voltage reference, the circuit including:

a. a first pair of transistors coupled to the non-inverting input of the amplifier, the first pair including a first and second transistor of the circuit, the bases of the first and second transistor being commonly coupled, the first transistor being additionally coupled to the amplifier output via a feedback resistor, the second transistor being provided in a diode configuration,

b. a second pair of transistors, the second pair including a third and fourth transistor of the circuit, the third transistor being coupled to the inverting input of the amplifier, the emitters of the third and fourth transistors being coupled to ground via a reference resistor, the fourth transistor being provided in a diode configuration and being coupled via a coupling resistor to the second transistor, and

wherein the base of the third transistor is coupled to the commonly coupled first and second transistors, the collector of the third transistor being coupled to the collector of the first transistor such that the first and third transistors form a preamplifier to the amplifier, and further wherein the emitter areas of the first and fourth transistors are scaled to be larger than that the emitter areas of the second and third transistors such that two base-emitter voltage differences, of the form of proportional to absolute temperature (PTAT) voltages, are developed across the coupling and feedback resistors respectively, the resultant PTAT currents generating a PTAT voltage across the reference resistor, this PTAT voltage in combination with the base emitter voltages of the combined second and third transistors being reflected at the output of the amplifier as a first order temperature insensitive voltage, and further wherein the circuit further includes;

a filter provided between the non-inverting input and ground to minimize high band noise contributions to this temperature insensitive voltage, and

a current shunt configured to shunt at least a portion of the feedback current away from the first transistor so as effect a reduction in the collector and base currents of the first and third transistors thereby reducing low band noise contributions to this order temperature insensitive voltage.

24. The circuit as claimed in claim 23 wherein the current shunt is configured to reduce the collector current of the first and third transistors and as a result to effect a reduction in the base currents of the first and third transistors.

25. The circuit as claimed in claim 24 wherein the current shunt includes two npn transistors and one pnp transistor, the pnp transistor forming a fifth transistor of the circuit, the two npn transistors forming sixth and seventh transistors of the circuit.

26. The circuit of claim 25 wherein the emitter areas of the transistors are chosen such that the second and third transistors have a first emitter area, n, the fourth transistor has a second emitter area n1, the first transistor has a third emitter area, n2, the fifth transistor has a fourth emitter area, n3, the sixth transistor has a fifth emitter area, n4 and the seventh transistor has a sixth emitter area, n5, the emitter areas being scaled such that n5>

n4>

n3>

n2>

n1>

n.

27. The circuit of claim 23 wherein the filter includes a capacitor.

28. The circuit of claim 27 wherein the capacitor has a value less than 1000 pF.

29. The circuit of claim 27 wherein the capacitor has a value less than 200 pF.

30. The circuit of claim 29 wherein the capacitor has a value of about 100 pF.

31. The circuit of claim 23 further including a curvature correction component.

32. The circuit of claim 31 wherein the curvature correction component is configured to provide a correction voltage of the type TlogT of opposite sign to that of the first order voltage reference voltage output, the correction voltage being combined with the first order voltage reference to provide a curvature corrected voltage reference.

33. The circuit of claim 27 wherein the capacitor is provided on-chip.

34. A bandgap reference circuit including an amplifier having an inverting and a non-inverting input and providing at its output a voltage reference, the non-inverting input being a high impedance input to the amplifier and wherein the circuit additionally includes a filter coupled between that high-impedance input and ground to filter high band noise at the input to the amplifier.

35. A bandgap reference circuit including a plurality of transistors arranged in a bandgap cell and coupled to an amplifier having an inverting and a non-inverting input and providing at its output a voltage reference, wherein the circuit includes a feedback loop between the output of the amplifier and transistors forming the bandgap cell and wherein the circuit additionally includes a shunt circuit configured to divert at last a portion of current from the feedback loop so as to reduce the collector emitter currents and hence the base currents of the transistors forming the bandgap cell.