Buck DC-DC converter with improved accuracy and stability

1. A buck switching regulator being configured to receiving an input voltage and to generate a regulated output voltage, the buck switching regulator controlling a high-side switch and a low-side switch based on a feedback control scheme to drive a switch output node for generating a switching output voltage, the switch output node being coupled to an LC filter to generate the regulated output voltage having a substantially constant magnitude on an output node, the buck switching regulator including a feedback control circuit comprising:

a balanced feedback network including first and second gain circuits configured to generate first and second feedback signals, respectively, indicative of the regulated output voltage;

a ripple generation circuit configured to generate a ripple signal using the switching output voltage and to inject a first ripple signal to the first gain circuit and a second ripple signal to the second gain circuit;

an operational transconductance amplifier (OTA) configured to receive the second feedback signal generated from the second gain circuit and a reference signal and to generate an output signal having a magnitude indicative of the difference between the second feedback signal and the reference signal, the output signal of the OTA being coupled to a node in the feedback control circuit; and

a comparator configured to receive at least the first feedback signal and a comparator reference signal and to generate a comparator output signal having an output level indicative of the difference between the first feedback signal and the comparator reference signal,

wherein the output signal of the OTA is applied to the feedback control circuit to cancel a voltage offset in the regulated output voltage due to the injected ripple signal to the first gain circuit.

2. The buck switching regulator of claim 1 , wherein the output signal of the OTA is coupled to the first gain circuit to adjust the first feedback signal and the comparator reference signal is the reference signal coupled to the OTA.

3. The buck switching regulator of claim 2 , wherein the output signal of the OTA is coupled to a first node in the first gain circuit at a node at which the first feedback signal is generated.

4. The buck switching regulator of claim 2 , wherein the output signal of the OTA is coupled to a first node in the first gain circuit below a second node at which the first feedback signal is generated, the first node being closer to the ground potential than the second node.

5. The buck switching regulator of claim 2 , wherein the output signal of the OTA is coupled to a first node in the first gain circuit above a second node at which the first feedback signal is generated, the second node being closer to the ground potential than the first node, and the resistance between the first node and the second node is less than the resistance between the second node and the ground potential.

6. The buck switching regulator of claim 1 , wherein the OTA has a low bandwidth and the output signal of the OTA rejects ripple and transient that may be present on the regulated output voltage.

7. The buck switching regulator of claim 1 , wherein the first feedback signal has the same magnitude or a different magnitude than the second feedback signal.

8. The buck switching regulator of claim 1 , wherein the first gain circuit comprises a voltage divider having a first divider ratio and the second gain circuit comprises a voltage divider having a second divider ratio, the first divider ratio being the same as or different from the second divider ratio.

9. The buck switching regulator of claim 8 , wherein the first gain circuit comprises:

first, second and third resistors connected in series between the output node and a ground potential, the first feedback signal being generated at a node between the first and second resistors, and the ripple generation circuit being configured to inject the first ripple signal to a node between the second and third resistors,

wherein the output signal of the OTA is coupled to the node between the second and third resistors and the comparator reference signal is the reference signal coupled to the OTA.

10. The buck switching regulator of claim 9 , wherein the second gain circuit comprises:

fourth, fifth and sixth resistors connected in series between the output node and a ground potential, the second feedback signal being generated at a node between the fourth and fifth resistors, and the ripple generation circuit being configured to inject the second ripple signal to a node between the fifth and sixth resistors,

wherein the OTA receives the second feedback signal and generates the output signal to be coupled to the node between the second and third resistors of the first gain circuit.

11. The buck switching regulator of claim 1 , further comprising:

a controller and driver circuit configured to drive the high-side switch and the low-side switch in response to the comparator output signal, the comparator output signal being asserted to turn on the high-side switch.

12. The buck switching regulator of claim 11 , wherein the comparator output signal is asserted when the first feedback signal is less than the comparator reference signal.

13. The buck switching regulator of claim 11 , wherein the controller and driver circuit implements a constant on-time feedback control scheme.

14. The buck switching regulator of claim 8 , wherein the first gain circuit comprises:

first, second, third and fourth resistors connected in series between the output node and a ground potential, the first feedback signal being generated at a node between the second and third resistors, and the ripple generation circuit being configured to inject the first ripple signal to a node between the third and fourth resistors,

wherein the output signal of the OTA is coupled to the node between the first and second resistors and the comparator reference signal is the reference signal coupled to the OTA, and the resistance of the second resistor is less than the sum of the resistance of the third and fourth resistors.

15. The buck switching regulator of claim 14 , wherein the second gain circuit comprises:

fifth, sixth, seventh and eighth resistors connected in series between the output node and a ground potential, the second feedback signal being generated at a node between the sixth and seventh resistors, and the ripple generation circuit being configured to inject the second ripple signal to a node between the seventh and eighth resistors,

wherein the OTA receives the second feedback signal and generates the output signal to be coupled to the node between the first and second resistors of the first gain circuit.

16. The buck switching regulator of claim 1 , wherein the output signal of the OTA is coupled to the comparator as the comparator reference signal.

17. The buck switching regulator of claim 1 , wherein the output signal of the OTA is coupled to the comparator to adjust the comparison level of the comparator.

18. A method in buck switching regulator receiving an input voltage and controlling a high-side switch and a low-side switch using a feedback control scheme to drive a switch output node for generating a switching output voltage, the switch output node being coupled to an LC filter circuit to generate a regulated output voltage having a substantially constant magnitude on an output node, the method comprising:

generating first and second feedback signals indicative of the regulated output voltage using first and second feedback networks, respectively;

generating first and second ripple signals using the switching output voltage;

injecting the first ripple signal to the first feedback network generating the first feedback signal;

injecting the second ripple signal to the second feedback network generating the second feedback signal;

generating using an operational transconductance amplifier (OTA) an output signal having a magnitude indicative the difference between the second feedback signal and a reference signal;

coupling the output signal of the OTA to a node in a feedback control loop to cancel a voltage offset in the regulated output voltage due to the injected ripple signal to the first feedback signal; and

generating using a comparator a comparator output signal having an output level indicative of the difference between the first feedback signal and a comparator reference signal.

19. The method of claim 18 , wherein the OTA has a low bandwidth and generating using an operational transconductance amplifier (OTA) an output signal having a magnitude indicative the difference between the second feedback signal and a reference signal comprises:

generating an output signal at the OTA which rejects ripple and transient that may be present on the regulated output voltage.

20. The method of claim 18 , wherein the first feedback signal has the same magnitude or a different magnitude than the second feedback signal.

21. The method of claim 18 , wherein generating first and second feedback signals indicative of the regulated output voltage using first and second feedback networks comprises:

dividing the regulated output voltage by a first divider ratio to generate the first feedback signal; and

dividing the regulated output voltage by a second divider ratio to generate the second feedback signal, the first divider ratio being the same as or different from the second divider ratio.

22. The method of claim 21 , wherein dividing the regulated output voltage by a first divider ratio to generate the first feedback signal comprises:

connecting first, second and third resistors in series between the output node and a ground potential, the first feedback signal being generated at a node between the first and second resistors, and the first ripple signal being injected to a node between the second and third resistors,

wherein the output signal of the OTA is coupled to the node between the second and third resistors and the comparator reference signal comprises the reference signal.

23. The method of claim 22 , wherein dividing the regulated output voltage by a second divider ratio to generate the second feedback signal comprises:

connecting fourth, fifth and sixth resistors in series between the output node and a ground potential, the second feedback signal being generated at a node between the fourth and fifth resistors, and the second ripple signal being injected to a node between the fifth and sixth resistors.

24. The method of claim 18 , further comprising:

driving the high-side switch and the low-side switch in response to the comparator output signal, the comparator output signal being asserted to turn on the high-side switch.

25. The method of claim 24 , wherein generating, using a comparator, a comparator output signal having an output level indicative of the difference between the first feedback signal and the reference signal comprises:

asserting the comparator output signal when the first feedback signal is less than the comparator reference signal.

26. The method of claim 24 , wherein driving the high-side switch and the low-side switch in response to the comparator output signal comprises:

driving the high-side switch and the low-side switch in response to the comparator output signal under a constant on-time feedback control scheme.

27. The method of claim 21 , wherein dividing the regulated output voltage by a first divider ratio to generate the first feedback signal comprises:

connecting first, second, third and fourth resistors in series between the output node and a ground potential, the first feedback signal being generated at a node between the second and third resistors, and the first ripple signal being injected to a node between the third and fourth resistors,

wherein the output signal of the OTA is coupled to the node between the first and second resistors and the comparator reference signal is the reference signal coupled to the OTA, and the resistance of the second resistor is less than the sum of the resistance of the third and fourth resistors.

28. The method of claim 27 , wherein dividing the regulated output voltage by a second divider ratio to generate the second feedback signal comprises:

connecting fifth, sixth, seventh and eighth resistors in series between the output node and a ground potential, the second feedback signal being generated at a node between the sixth and seventh resistors, and the second ripple signal being injected to a node between the seventh and eighth resistors.

29. The method of claim 18 , wherein coupling the output signal of the OTA to a node in a feedback control loop comprises:

coupling the output signal of the OTA to the comparator as the comparator reference signal.

30. The method of claim 18 , wherein coupling the output signal of the OTA to a node in a feedback control loop comprises:

coupling the output signal of the OTA to the comparator to adjust the comparison level of the comparator.