High accuracy zener based voltage reference circuit
A voltage reference circuit is disclosed comprising: a supply terminal; a ground terminal; a first current source and a Zener diode connected in series between the supply and ground terminals and having a first node therebetween and configured to supply a Zener voltage at the first node; an output node configured to provide a voltage reference; and a CTAT, circuit connected between the first node and the output node; wherein the CTAT circuit comprises: two bipolar transistors, having their respective emitters connected at a second node, and configured to, in operation, have equal collector-emitter currents, the base of the first bipolar transistor being connected to the first node, the base of the second bipolar transistor being connected to a centre node of a first voltage divider; and wherein the first voltage divider is connected between the emitter of the second bipolar transistor and the output node.
1. A voltage reference circuit comprising:
a supply terminal configured to be connected to a supply voltage;
a ground terminal configured to be connected to a ground voltage;
a first current source and a Zener diode connected in series between the supply terminal and the ground terminal and having a first node therebetween and configured to supply a Zener voltage at the first node;
an output node configured to provide a voltage reference; and
a complementary to absolute temperature, CTAT, circuit connected between the first node and the output node;
wherein the CTAT circuit comprises:
a first bipolar transistor and a second bipolar transistor, each having a base, a collector and an emitter, having their respective emitters connected at a second node, and configured to, in operation, have equal collector-emitter currents,
wherein the base of the first bipolar transistor is connected to the first node and the base of the second bipolar transistor is connected to a centre node of a first voltage divider, and
wherein the first voltage divider consists of a first resistance connected between the output node and the centre node and a second resistance connected between the centre node and the emitter of the second bipolar transistor.
2. A voltage reference circuit as claimed in claim 1 , wherein the CTAT circuit further comprises a second current source, connected between the collector of the first bipolar transistor and the supply node, and configured to provide a bias current to the first bipolar transistor.
3. A voltage reference circuit as claimed in claim 1 , wherein the CTAT circuit further comprises a FET having main terminals connected between the collector of the second bipolar transistor and the supply node, and a control terminal connected to the collector of the first bipolar transistor, and configured to match the collector-emitter currents through the first and second bipolar transistors.
4. A voltage reference circuit as claimed in claim 1 , wherein the CTAT circuit further comprises a third current source, connected between the emitters of the first and second bipolar transistors, and the ground terminal.
5. A voltage reference circuit as claimed in claim 1 , wherein the third current source is configured to sink a current equal to twice that supplied by the second current source plus a current through the second resistor.
6. A voltage reference circuit as claimed in claim 1 , wherein the voltage reference is provided directly at the output node.
7. A voltage reference circuit as claimed in claim 1 , further comprising a second voltage divider comprising two resistors connected between the output node and ground and having a centre node therebetween, wherein the voltage reference is at the centre node of the second voltage divider.
8. A voltage reference circuit as claimed in claim 1 , wherein the first bipolar transistor and the second bipolar transistor are each NPN transistors.
9. A voltage reference circuit as claimed in claim 1 , wherein the first bipolar transistor and second bipolar transistor are matched transistors.
10. A voltage reference circuit as claimed in claim 1 , wherein the current through the first voltage divider is less than 100 nA.
11. A voltage reference circuit as claimed in claim 3 , configured to operate with a minimum supply voltage which is the sum of the Zener voltage and a gate-source voltage across the FET.
12. A voltage reference circuit as claimed in claim 1 , configured to operate with a supply voltage between 6 V and 7 V.
13. A voltage reference circuit as claimed in claim 1 , wherein the second current source and the third current source are each configured to have a zero temperature coefficient, OTC.
14. A voltage reference circuit as claimed in claim 4 , wherein the third current source is configured to sink a current consisting of a proportional to absolute temperature, PTAT, component and a CTAT component, wherein the CTAT component is a scaled version of a current through the second resistor.
15. A voltage reference circuit as claimed in claim 1 , wherein the CTAT circuit further comprises a third current source, connected between the emitters of the first and second bipolar transistors, and the ground terminal.
16. A voltage reference circuit comprising:
a supply terminal configured to be connected to a supply voltage;
a ground terminal configured to be connected to a ground voltage;
a first current source and a Zener diode connected in series between the supply terminal and the ground terminal and having a first node therebetween and configured to supply a Zener voltage;
an output node configured to provide the voltage reference; and
a complementary to absolute temperature, CTAT, circuit connected between the first node and the output node;
wherein the CTAT circuit comprises a first bipolar transistor and a second bipolar transistor having matched emitter currents wherein the first bipolar transistor is configured to receive the Zener voltage at its base, and the voltage reference is derived from a voltage at the base of the second bipolar transistor.
17. The voltage reference circuit of claim 16 , wherein
the first bipolar transistor and the second bipolar transistor, each having a base and a collector and an emitter, with their respective emitters connected at a second node, wherein
the collector of the first transistor is connected to the supply terminal by a second current source,
the collector of the second transistor is connected to the output node, and to the supply terminal through a FET,
and the base of the first bipolar transistor is connected to the first node;
a voltage divider connected in parallel with the second bipolar transistor and having a centre node connected to the base of the second transistor, a lower terminal connected to the second node, and
an upper terminal connected to the output node; and
a third current source connected between the ground terminal and the second node.
18. The voltage reference circuit of claim 17 , further comprising a second voltage divider comprising two resistors connected between the output node and ground and having a centre node therebetween, wherein the voltage reference is at the centre node of the second voltage divider.
19. The voltage reference circuit of claim 18 , wherein the CTAT circuit further comprises a second current source, connected between the collector of the first bipolar transistor and the supply node, and configured to provide a bias current to the first bipolar transistor.
20. The voltage reference circuit of claim 18 , wherein the CTAT circuit further comprises a third current source, connected between the emitters of the first and second bipolar transistors, and the ground terminal.