Reference voltage source and method for providing a curvature-compensated reference voltage
A reference voltage source comprises a bandgap voltage reference circuit having a first node and an output node, the output node being arranged for providing a reference voltage. A curvature correction circuit has an input node connected to the output node and/or to a base of a first bipolar device of the bandgap voltage reference circuit and/or to a base of a second bipolar device of the bandgap voltage reference circuit. The curvature correction circuit has an output node connected to the first node of the bandgap voltage reference circuit. The curvature correction circuit comprises a current source for providing a current having a different temperature dependency than a temperature dependency of a first current through the first bipolar device of the bandgap voltage reference circuit.
1. A reference voltage source, comprising:
a bandgap voltage reference circuit having a first node and an output node, the output node being arranged for providing a reference voltage; and
a curvature correction circuit having an input node connected to one or more of the output node, a base of a first bipolar device of the bandgap voltage reference circuit, and a base of a second bipolar device of the bandgap voltage reference circuit, wherein;
the curvature correction circuit comprises an output node connected to the first node of the bandgap voltage reference circuit,
the curvature correction circuit comprises a current source for providing a current having a different temperature dependency than a temperature dependency of a first current through the first bipolar device of the bandgap voltage reference circuit; and
wherein the current source comprises a modified Wilson current mirror, wherein a gate of a control transistor of the modified Wilson current mirror is connected to a collector of a third bipolar device and an output node of the modified Wilson current mirror is connected to an emitter of the third bipolar device.
2. The reference voltage source of claim 1 , wherein the first and the second bipolar device are arranged to work with different emitter current densities, and an emitter of the first bipolar device or an emitter of the second bipolar device is connected to the first node.
3. The reference voltage source of claim 1 , wherein the first node is arranged between an emitter of the first bipolar device and an emitter of the second bipolar device.
4. The reference voltage source of claim 1 , wherein the base of at least one of the first bipolar device and the second bipolar device and the third bipolar device is connected to the output node of the bandgap voltage reference circuit.
5. The reference voltage source of claim 1 , wherein the reference voltage source comprises a feedback control having a first and a second input terminal, wherein the first input terminal is arranged to be fed by a signal representative for a strength of a collector current through the first bipolar device, wherein the second input terminal is arranged to be fed by a signal representative for a strength of a collector current through the second bipolar device, wherein an output terminal of the feedback control is connected to a base of the first bipolar device and to a base of the second bipolar device.
6. The reference voltage source of claim 1 , wherein the current source comprises a Vbe/R bias source.
7. The reference voltage source of claim 1 , wherein the current source comprises a current source for providing an output current, which is proportional to absolute temperature.
8. The reference voltage source of claim 2 , wherein the third bipolar device is arranged to work at a reference temperature T R with a same emitter current density as the emitter current density of the first bipolar device or of the second bipolar device.
9. The reference voltage source of claim 2 , wherein the bandgap voltage reference circuit comprises a second resistor between the emitter of the first bipolar device and the emitter of the second bipolar device.
10. The reference voltage source of claim 3 , wherein the bandgap voltage reference circuit comprises a first resistor between the emitter of the first bipolar device and a first terminal of a power supply.
11. The reference voltage source of claim 6 , wherein the reference voltage source comprises a circuit for controlling an input current of the Vbe/R bias source in dependency of a strength of at least one of the collector current through the first bipolar device and the collector current through the second bipolar device.
12. The reference voltage source of claim 7 , wherein the reference voltage source comprises a circuit for controlling the output current, which is proportional to absolute temperature in dependency of a strength of at least one of the collector current through the first bipolar device and the collector current through the second bipolar device.
13. The reference voltage source of claim 7 , wherein the current source comprises a node for summing up an output current of the Vbe/R bias source and the output current of the current source for providing a current which is temperature independent.
14. The reference voltage source of claim 10 , wherein a base of the third bipolar device is connected to the output node of the bandgap voltage reference circuit.
15. The reference voltage source of claim 14 , wherein a third resistor forms a link between an emitter of the third bipolar device and the first node of the reference voltage source.
16. The reference voltage source of claim 15 , wherein a ratio of the value of the third resistor divided by the value of the first resistor is (x 1 −x 3 )/(n−x 1 ); wherein x 1 represents a power of temperature dependency of the collector current of the first bipolar device under operating conditions; wherein x.sub.3 represents a power of temperature dependency of the collector current of the third bipolar device under operating conditions; and wherein n has the value of 4 minus a power of a temperature dependency of a mobility for minority carriers.
17. A method of providing a reference voltage, comprising:
providing a first collector current through a collector of a first bipolar device, wherein a value of the first collector current has a first temperature dependency, wherein the first collector current causes a first current density at an emitter of the first bipolar device;
providing a second collector current through a collector of a second transistor, wherein the second collector current causes at an emitter of the second bipolar device a second current density, wherein the second current density is lower than first current density; and
providing a third current through a collector of a third bipolar device, the third current provided by a modified Wilson current mirror connected to an emitter of the third bipolar device, wherein a gate of a control transistor of the modified Wilson current mirror is connected to the collector of the third bipolar device, and wherein a value of the third current has a second temperature dependency, wherein the second temperature dependency is different to the first temperature dependency.
18. A reference voltage source, comprising:
a bandgap voltage reference circuit having a first bipolar device, a second bipolar device, a first node and an output node, the output node being arranged for providing a reference voltage; and
a curvature correction circuit having a third bipolar device, a base of the third bipolar device connected to the output node, a base of the first bipolar device, and a base of the second bipolar device, wherein:
the curvature correction circuit comprises an output node connected to the first node of the bandgap voltage reference circuit, and
the curvature correction circuit comprises a current source for providing a current having a different temperature dependency than a temperature dependency of a first current through the first bipolar device of the bandgap voltage reference circuit.
19. The reference voltage source of claim 18 , wherein the first and the second bipolar device are arranged to work with different emitter current densities, and an emitter of the first bipolar device or an emitter of the second bipolar device is connected to the first node.
20. The reference voltage source of claim 19 , wherein the curvature correction circuit comprises a third bipolar device, wherein the third bipolar device is arranged to work at a reference temperature T R with a same emitter current density as the emitter current density of the first bipolar device or of the second bipolar device.