Analog supply generation using low-voltage digital supply

1. An apparatus, comprising:

a first reference circuit configured to generate, using a voltage level of an input power supply node, a first reference voltage with a first tolerance value;

a second reference circuit configured to generate, using a voltage level of a regulated power supply node, a second reference voltage with a second tolerance value less than the first tolerance value; and

a device configured, in response to an activation of a startup signal, to generate a first voltage on a first internal power supply node using the voltage level of the input power supply node and the first reference voltage;

a first charge pump circuit configured to generate a second voltage on a second internal power supply node using a clock signal and a voltage level of the first internal power supply node; and

a second charge pump circuit configured to generate a particular voltage level on the regulated power supply node using the voltage level of the second internal power supply node, and the clock signal; and

wherein the device is further configured, in response to a determination that a particular time period has elapsed since the activation of the startup signal, to generate the first voltage on the first internal power supply node using the voltage level of the input power supply node and the second reference voltage.

2. The apparatus of claim 1 , further comprising:

a third charge pump circuit coupled in parallel with the first charge pump circuit; and

a fourth charge pump circuit coupled in parallel with the second charge pump circuit.

3. The apparatus of claim 1 , further comprising a feedback circuit configured to:

generate, in response to the activation of the startup signal, a feedback signal such that a voltage level of the feedback signal is offset from a voltage level of the regulated power supply node by a diode voltage drop; and

divide, in response to the determination that the particular time period has elapsed, the feedback signal such that the voltage level of the feedback signal is a fraction of the voltage level of the regulated power supply node.

4. The apparatus of claim 3 , further comprising a comparator circuit configured to:

compare, in response to the activation of the startup signal, the first reference voltage to the feedback signal to generate a control signal; and

compare, in response to determining the particular time period has elapsed, the second reference voltage to the feedback signal to generate the control signal; and

wherein the device is further configured to generate the first voltage on the first internal power supply node using the control signal.

5. The apparatus of claim 1 , wherein the second reference circuit includes a bandgap reference circuit.

6. A method, comprising:

generating a first reference voltage using a voltage level of an input power supply node;

generating, by a power converter circuit that includes a plurality of charge pump circuits, a first voltage level on a first internal power supply node using the voltage level of the input power supply node and a control signal;

generating, by a first charge pump circuit of the plurality of charge pump circuits, a second voltage on a second internal power supply node using a clock signal and the voltage level of the first internal power supply node;

generating, by a second charge pump circuit of the plurality of charge pump circuits during a first time period, a particular voltage level on a regulated power supply node using the voltage level of the second internal power supply node, and the clock signal;

generating a second reference voltage using a voltage level of the regulated power supply node, wherein a first tolerance of the first reference voltage is greater than a second tolerance of the second reference voltage; and

generating, by the power converter circuit during a second time period subsequent to the first time period, the particular voltage level on the regulated power supply node using the voltage level of the input power supply node and the second reference voltage.

7. The method of claim 6 , further comprising:

generating, during the first time period, the control signal using the first reference voltage; and

generating, during the second time period, the control signal using the second reference voltage.

8. The method of claim 6 , wherein generating the first voltage level on the first internal power supply node includes:

comparing, during the second time period, the second reference voltage to a feedback signal to generate the control signal; and

adjusting a conductance between the input power supply node and the first internal power supply node.

9. The method of claim 8 , further comprising:

coupling, during the first time period, the regulated power supply node to a diode to generate the feedback signal; and

coupling, during the second time period, the regulated power supply node to a resistive voltage divider circuit to generate the feedback signal.

10. The method of claim 8 , further comprising generating the clock signal using the voltage level of the first internal power supply node.

11. The method of claim 6 further comprising, generating the second reference voltage using a bandgap reference circuit.

12. An apparatus, comprising:

a functional circuit coupled to a regulated power supply node; and

a power converter circuit that includes a plurality of charge pump circuits, a first internal power supply node, and a second internal power supply node, and wherein the power converter circuit is configured to:

generate a first reference voltage using a voltage level of an input power supply node;

in response to receiving an activation signal:

generate a first voltage level on the first internal power supply node using the voltage level of the input power supply node and a control signal;

generate, using a first charge pump circuit of the plurality of charge pump circuits, a second voltage on the second internal power supply node using a clock signal and the voltage level of the first internal power supply node;

generate, using a second charge pump circuit of the plurality of charge pump circuits, a particular voltage level on the regulated power supply node using a voltage level of the second internal power supply node, and the clock signal;

generate a second reference voltage using a voltage level of the regulated power supply node, wherein a first tolerance of the first reference voltage is greater than a second tolerance of the second reference voltage; and

in response to a determination that a particular time period has elapsed, generate the particular voltage level on the regulated power supply node using the voltage level of the input power supply node and the second reference voltage.

13. The apparatus of claim 12 , wherein the power converter circuit is further configured to:

generate, in response to receiving the activation signal, the control signal using the first reference voltage; and

generate, in response to the determination the particular time period has elapsed, the control signal using the second reference voltage.

14. The apparatus of claim 12 , wherein to generate the first voltage level on the first internal power supply node, the power converter circuit is further configured to:

compare, after the particular time period has elapsed, the second reference voltage to a feedback signal to generate the control signal; and

adjust a conductance between the input power supply node and the first internal power supply node.

15. The apparatus of claim 14 , wherein the power converter circuit includes:

a non-linear circuit configured, in response to receiving the activation signal, to subtract an offset from the voltage level of the regulated power supply node to generate the feedback signal; and

a resistive voltage divider circuit configured, in response to the determination that the particular time period has elapsed, to divide the voltage level of the regulated power supply node to generate the feedback signal.

16. The apparatus of claim 14 , wherein the power converter circuit is further configured to generate the clock signal using the voltage level of the first internal power supply node.

17. The apparatus of claim 12 , wherein the power converter circuit includes a bandgap reference circuit configured to generate the second reference voltage.