Programmable fractional charge pump for DC-DC converter
View Patent ↗A charge pump provides a programmable multiplication factor for generating an output voltage. A first output voltage may be generated by connecting a first plurality of N capacitors in a first plurality of (N+1) configurations. A second output voltage may be generated by connecting a second plurality of M capacitors in a second plurality of M+1 configurations. The first plurality of N capacitors and the second plurality of M capacitors have one or more capacitors in common. The integers M and N may be equal, although this is not required. The first plurality of configurations is different than the second plurality of configurations, thereby providing different multiplication factors for the first and second pluralities of configurations. In one embodiment, the first plurality of (N+1) configurations results in an output voltage of about 3/4× an input voltage.
1. A programmable charge pump comprising:
a first terminal configured to receive a first supply voltage
a second terminal configured to receive a second supply voltage;
an output terminal configured to provide an output voltage;
a first capacitor;
a second capacitor; and
interconnection circuitry for wiring the first capacitor and the second capacitor in a first configuration, a second configuration and a third configuration,
wherein in the first configuration, the first capacitor is coupled in series between the first terminal and the output terminal, but the second capacitor is not coupled in series between the first terminal and the output terminal,
wherein in the second configuration, the first and second capacitors are coupled in series between the second terminal and the output terminal, and
wherein in the third configuration, the first and second capacitors are coupled in series between the first terminal and the output terminal.
2. The charge pump of claim 1 , wherein the first capacitor has a first orientation with respect to the first terminal in the first configuration, and a second orientation, opposite the first orientation, with respect to the first terminal in the third configuration.
3. The charge pump of claim 2 , wherein the first capacitor has a first orientation with respect to the output terminal in the first configuration, and a second orientation, opposite the first orientation, with respect to the output terminal in the second and third configurations.
4. The charge pump of claim 2 , wherein the second capacitor has a first orientation with respect to the output terminal in the second configuration, and a second orientation, opposite the first orientation, with respect to the output terminal in the third configuration.
5. A programmable charge pump comprising:
a first terminal configured to receive a first supply voltage
a second terminal configured to receive a second supply voltage;
an output terminal configured to provide an output voltage;
a first capacitor;
a second capacitor; and
interconnection circuitry for wiring the first capacitor and the second capacitor in a first configuration, a second configuration and a third configuration,
wherein in the first configuration, the first capacitor is coupled in series between the first terminal and the output terminal, and the first and second capacitors are coupled in series between the first terminal and the second terminal,
wherein in the second configuration, the first and second capacitors are coupled in series between the second terminal and the output terminal, and
wherein in the third configuration, the first and second capacitors are coupled in series between the first terminal and the output terminal.
6. The charge pump of claim 5 , wherein the second capacitor has the same orientation with respect to the first terminal in the first and third configurations.
7. A programmable charge pump comprising:
a first terminal configured to receive a first supply voltage
a second terminal configured to receive a second supply voltage;
an output terminal configured to provide an output voltage wherein the output voltage is about 0.75 times the first supply voltage;
a first capacitor;
a second capacitor; and
interconnection circuitry for wiring the first capacitor and the second capacitor in a first configuration, a second configuration and a third configuration,
wherein in the first configuration, the first capacitor is coupled in series between the first terminal and the output terminal,
wherein in the second configuration, the first and second capacitors are coupled in series between the second terminal and the output terminal, and
wherein in the third configuration, the first and second capacitors are coupled in series between the first terminal and the output terminal.
8. A programmable charge pump comprising:
a first terminal configured to receive a first supply voltage
a second terminal configured to receive a second supply voltage;
an output terminal configured to provide an output voltage;
a first capacitor;
a second capacitor; and
interconnection circuitry for wiring the first capacitor and the second capacitor in a first configuration, a second configuration and a third configuration,
wherein in the first configuration, the first capacitor is coupled in series between the first terminal and the output terminal,
wherein in the second configuration, the first and second capacitors are coupled in series between the second terminal and the output terminal, and the first and second capacitors are isolated from the first terminal, and
wherein in the third configuration, the first and second capacitors are coupled in series between the first terminal and the output terminal.
9. The charge pump of claim 1 , wherein in the third configuration, the first and second capacitors are isolated from the second terminal.
10. The charge pump of claim 1 , further comprising an output capacitor which remains coupled to the output terminal in the first, second and third configurations.
11. The charge pump of claim 1 , further comprising control logic for cycling the charge pump through the first, second and third configurations in a repeating sequence.
12. A method of operating a charge pump comprising:
receiving a first voltage on a first input terminal;
receiving a second voltage on a second input terminal;
providing an output voltage on an output terminal;
coupling a first capacitor and a second capacitor in a first configuration, wherein the first capacitor is coupled in series between the first input terminal and the output terminal;
coupling the first capacitor and the second capacitor in a second configuration, wherein the first and second capacitors are coupled in series between the second input terminal and the output terminal;
coupling the first capacitor and the second capacitor in a third configuration, wherein the first and second capacitors are coupled in series between the first input terminal and the output terminal, wherein the output voltage provided on the output terminal is less than the first voltage.
13. The method of claim 12 , further comprising coupling the first capacitor and the second capacitor in series between the first and second input terminals in the first configuration.
14. The method of claim 12 , further comprising coupling the first capacitor in a first orientation with respect to the first input terminal in the first configuration, and coupling the first capacitor in a second orientation, opposite the first orientation, with respect to the first input terminal in the third configuration.
15. The method of claim 14 , further comprising coupling the first capacitor in a first orientation with respect to the output terminal in the first configuration, and coupling the first capacitor in a second orientation, opposite the first orientation, with respect to the output terminal in the second and third configurations.
16. The method of claim 14 , further comprising coupling the second capacitor in a first orientation with respect to the output terminal in the second configuration, and coupling the second capacitor in a second orientation, opposite the first orientation, with respect to the output terminal in the third configuration.
17. The method of claim 12 , further comprising de-coupling the first and second capacitors from the first input terminal during in the second configuration.
18. The method of claim 12 , wherein the average output voltage provided at the output terminal is substantially equal to 3/4 the first voltage.
19. The method of claim 12 , further comprising coupling an output capacitor to the output terminal in the first, second and third configurations.
20. The method of claim 12 , further comprising cycling through the first, second, and third configurations in a repeating sequence.
21. A method of designing a charge pump comprising:
selecting a number (N) of capacitors to implement the charge pump, wherein N is greater than or equal to two;
modeling N+1 operating phases of the charge pump with N+1 corresponding linear equations, wherein each of the N+1 linear equations includes an input voltage of the charge pump, an output voltage of the charge pump, N capacitor voltages, each associated with a corresponding one of the N capacitors, and coefficients associated with the input voltage, the output voltage and the N capacitor voltages, wherein each of the coefficients identifies a corresponding configuration of the input voltage, the output voltage and the capacitor voltages, and wherein the N+1 linear equations define a linear system;
assigning a plurality of different sets of coefficients to the N+1 linear equations; solving the N+1 linear equations for each of the different sets of coefficients, thereby obtaining a charge pump multiplication factor that identifies a ratio of the input voltage to the output voltage for each of the different sets of coefficients;
monitoring the charge pump multiplication factors obtained from each of the different sets of coefficients to identify charge pump multiplication factors that exist within a desired range.
22. The method of claim 21 , wherein the step of assigning a plurality of different sets of coefficients to the N+1 linear equations comprises randomly assigning a plurality of different sets of coefficients to the N+1 linear equations.
23. The method of claim 21 , wherein a coefficient associated with the input voltage identifies whether or not an input terminal configured to receive the input voltage is coupled or de-coupled from the charge pump in the associated operating phase, and wherein a coefficient associated with the output voltage identifies whether or not an output terminal configured to provide the output voltage is coupled or de-coupled from the charge pump in the associated operating phase.
24. The method of claim 22 , wherein the coefficients associated with the input and output voltages are binary values.
25. The method of claim 23 , wherein coefficients associated with the capacitor voltages identify whether the corresponding capacitors are connected in a first orientation between the input terminal and the output terminal, connected in a second orientation, opposite the first orientation, between the input terminal and the output terminal, or de-coupled from a path between the input terminal and the output terminal.
26. The method of claim 23 , wherein the coefficients associated with the capacitor voltages are 1, 0 and −1.