Circuits and methods for amplifying signals
View Patent ↗The present invention discloses a bus pumping compensation for a pulse modulation circuit such as class D modulators. The compensation according to the present invention provides a compensation current controlled by the output voltage, with the compensation characteristics matching the reverse current for improving circuit efficiency. Embodiments of the present invention also disclose a designable compensation circuit, comprising a linear compensation current, offering a good trade-off between circuit efficiency and ease of design. The present invention compensation circuit is preferably employed in a class D amplifier with substantial reverse current, and most preferably added into a LDO power supply in a class D amplifier circuit to prevent reverse current problem. The disclosed class D amplifier circuit is preferably used in an audio media player.
1. A method for compensating for reverse power supply current of a modulator, the method comprising:
generating a voltage-dependent compensation current for the power supply to compensate for the reverse current, the compensation current controlled by an output voltage of the modulator circuit.
2. A method as in claim 1 wherein the reverse current is compensated by providing a higher magnitude of the compensation current than that of the reverse current for a predetermined range of output voltages.
3. A method as in claim 1 wherein the magnitude of the compensation current is always higher than the magnitude of the reverse current for the whole range of operating output voltages of the modulator circuit.
4. A method as in claim 1 wherein the relationship between the compensation current and the output voltage matches a reverse IV relationship between the reverse current and the output voltage for a predetermined range of output voltages.
5. A method as in claim 4 wherein the matching comprises a degree of similarity between the two relationships.
6. A compensation circuit coupled to a power supply and to a modulator circuit,
wherein the power supply provides power to the modulator circuit, and
wherein the modulator circuit comprises an output,
the compensation circuit sinking current on a pattern in which the compensation circuit sinks in one mode and does not sink in another mode.
7. A circuit as in claim 6 wherein the sinking current of the compensation circuit compensates for a reverse current to the power supply from the modulator circuit for a predetermined range of output voltages.
8. A circuit as in claim 6 wherein the reverse current is compensated by providing a sinking current having a higher magnitude than that of the reverse current.
9. A compensation circuit for compensating a reverse current of a power supply in a modulator circuit, the compensation circuit comprising:
a voltage-dependent load coupled to the power supply, the voltage-dependent load controlled by an output voltage of the modulator circuit;
wherein the compensation load is controlled by the output voltage with a compensation IV relationship comprising:
a zero compensation current section corresponding to a positive output voltage,
a constant compensation current section corresponding to a negative output voltage, and
a transition compensation current section connecting the zero compensation current section and the constant compensation current section.
10. A circuit as in claim 9 wherein the magnitude of the constant compensation current is higher than that of the maximum reverse current.
11. A circuit as in claim 9 wherein the transition compensation current is substantially linear from the constant compensation current to the zero compensation current.
12. A circuit as in claim 9 wherein the slope of the transition compensation current matches that of the reverse current.
13. A circuit as in claim 9 wherein the transition from the transition compensation current to the zero compensation current is in the vicinity of the zero output voltage of the modulator circuit.
14. A compensation circuit for compensating a reverse current of a power supply in a modulator circuit, the compensation circuit comprising:
a compensation load coupled to the power supply;
a control circuit to control a compensation current through the compensation load, the control circuit comprising:
a linear amplifier circuit having an input coupled to the output voltage of the modulator circuit and a control output coupled to the compensation load;
a clamping circuit coupled to the control output and to the compensation load to limit a compensation current through the compensation load between a constant value and zero value.
15. A circuit as in claim 14 wherein the power supply is a LDO power supply.
16. A circuit as in claim 14 wherein the modulator circuit comprises a single-ended load.
17. A circuit as in claim 14 wherein the modulator circuit comprises a single or a dual class D amplifier.
18. A circuit as in claim 14 wherein the compensation load comprises a resistor.
19. A circuit as in claim 14 wherein the linear amplifier circuit comprises an operational amplifier.
20. A circuit as in claim 14 further comprising a voltage divider circuit coupled between the output voltage of the modulator circuit and the input of the linear amplifier.
21. A circuit as in claim 14 wherein the clamping circuit comprises a transistor device.
22. A class D amplifier comprising a compensation circuit for compensating a reverse current of a power supply coupled to the amplifier, the compensation circuit coupled to the power supply and to the amplifier and sinking current on a pattern in which the compensation circuit sinks in one mode and does not sink in another mode.
23. A class D amplifier comprising a compensation circuit for compensating a reverse current of a power supply coupled to the amplifier, the compensation circuit comprising:
a compensation load coupled to the power supply;
a control circuit to control a compensation current through the compensation load, the control circuit comprising:
a linear amplifier circuit having an input coupled to the output voltage of the amplifier and a control output coupled to the compensation load;
a clamping circuit coupled to the control output and to the compensation load to limit a compensation current through the compensation load between a constant value and zero value.
24. A processor coupled to a class D amplifier, the processor presenting media through the class D amplifier, the class D amplifier comprising:
a compensation circuit for compensating a reverse current of a power supply coupled to the amplifier,
the compensation circuit coupled to the power supply and to the amplifier and sinking current on a pattern in which the compensation circuit sinks in one mode and does not sink in another mode.
25. A media player comprising a class D amplifier, the class D amplifier comprising:
a compensation circuit for compensating a reverse current of a power supply coupled to the amplifier,
the compensation circuit coupled to the power supply and to the amplifier and sinking current on a pattern in which the compensation circuit sinks in one mode and does not sink in another mode.
26. A media player comprising a class D amplifier, the class D amplifier comprising a compensation circuit for compensating a reverse current of a power supply coupled to the amplifier, the compensation circuit comprising:
a compensation load coupled to the power supply;
a control circuit to control a compensation current through the compensation load, the control circuit comprising:
a linear amplifier circuit having an input coupled to the output voltage of the amplifier and a control output coupled to the compensation load;
a clamping circuit coupled to the control output and to the compensation load to limit a compensation current through the compensation load between a constant value and zero value.