Methods and apparatus for an amplifier circuit

1. An integrated circuit, comprising:

a first operational amplifier (op-amp) comprising:

a non-inverting input terminal;

an inverting input terminal; and

an output terminal; and

a inverting amplifier circuit connected to the first operational amplifier and comprising:

a second operational amplifier (op-amp) comprising:

an inverting input terminal connected to the output terminal of the first operational amplifier; and

an output terminal connected to the non-inverting terminal of the first operational amplifier; and

at least one of a first resistor and a first capacitor, wherein the at least one of the resistor and the capacitor is connected between the output terminal of the second operational amplifier and the inverting terminal of the second operational amplifier.

2. The integrated circuit according to claim 1 , further comprising a second resistor and a second capacitor connected directly between the output terminal of the second op-amp and the non-inverting terminal of the first op-amp; wherein the second resistor and the second capacitor are connected in parallel with each other.

3. The integrated circuit according to claim 1 , wherein the second op-amp further comprises a non-inverting input terminal connected to a reference voltage.

4. The integrated circuit according to claim 1 , further comprising:

a second resistor connected between the output terminal of the first op-amp and the inverting terminal of the first op-amp; and

a second capacitor connected between the output terminal of the first op-amp and the inverting terminal of the first op-amp, wherein the second capacitor is connected in parallel with the second resistor.

5. The integrated circuit according to claim 1 , further comprising a second resistor connected directly between the output terminal of the first op-amp and the inverting terminal of the second op-amp.

6. The integrated circuit according to claim 1 , wherein a gain of the second op-amp is 1.

7. The integrated circuit according to claim 1 , further comprising:

a second resistor connected to the output terminal of the second op-amp; and

a second capacitor connected to the output terminal of the second op-amp and the non-inverting terminal of the first op-amp;

wherein the second resistor is further connected to:

the inverting terminal of the first op-amp via a third capacitor and a third resistor; and

the non-inverting terminal of the first op-amp via a fourth resistor.

8. The integrated circuit according to claim 1 , wherein the integrated circuit is configured to:

receive differential input signals; and

generate a single-ended output.

9. A method for removing distortion in an output signal of a digital-to-analog converter (DAC), comprising:

reducing an amplitude of a first input signal at an inverting terminal of a first operational amplifier (op-amp) comprising:

generating a first feedback signal according to an output signal of the first op-amp; and

transmitting the first feedback signal to the inverting terminal of the first op-amp; and

reducing an amplitude of a second input signal at a non-inverting terminal of the first op-amp comprising:

generating, with an inverting amplifier circuit, a second feedback signal according to the output signal of the first op-amp; and

transmitting the second feedback signal to the non-inverting terminal of the first op-amp.

10. The method according to claim 9 , wherein: the first input signal and the second input signal form a differential pair; and the output signal is a single-ended output.

11. The method according to claim 9 , the amplitude of the first input signal is substantially zero and the amplitude of the second input signal is substantially zero.

12. The method according to claim 9 , wherein the inverting amplifier circuit comprises:

a second operational amplifier comprising:

an inverting input terminal connected to an output terminal of the first operational amplifier;

a non-inverting terminal connected to a reference voltage; and

an output terminal connected to the non-inverting terminal of the first operational amplifier.

13. The method according to claim 9 , further comprising adjusting a gain of the inverting amplifier circuit.

14. An audio system, comprising:

an integrated circuit configured to receive a first analog input signal, and comprising:

processing circuitry configured to convert the first analog input signal into a digital signal; and

a digital-to-analog converter connected to the processing circuitry and comprising:

a digital circuit configured to process the digital signal; and

an analog circuit connected to an output terminal of the digital circuit, and comprising:

a switched-capacitor circuit; and

a output buffer comprising:

 a first operational amplifier comprising:

 a non-inverting input terminal;

 an inverting input terminal; and

 an output terminal to transmit a second analog signal; and

a second operational amplifier comprising:

 an inverting input terminal connected to the output terminal of the first operational amplifier; and

 an output terminal connected to the non-inverting terminal of the first operational amplifier;

a power amplifier connected to an output terminal of the output buffer and configured to increase a gain of the second analog signal; and

a speaker in communication with the amplifier and responsive to the second analog signal.

15. The audio system according to claim 14 , wherein the output buffer further comprises:

a first resistor connected between the output terminal of the second operational amplifier and the inverting terminal of the second operational amplifier; and

a first capacitor connected between the output terminal of the second operational amplifier and the inverting terminal of the second operational amplifier, wherein the capacitor is connected in parallel with the resistor.

16. The audio system according to claim 14 , further comprising a second resistor and a second capacitor; wherein:

the second resistor and the second capacitor are connected directly between the output terminal of the second op-amp and the non-inverting terminal of the first op-amp; and

the second resistor and the second capacitor are connected in parallel with each other.

17. The audio system according to claim 14 , wherein the second op-amp further comprises a non-inverting input terminal connected to a reference voltage.

18. The audio system according to claim 14 , further comprising a second resistor connected directly between the output terminal of the first op-amp and the inverting terminal of the second op-amp.

19. The audio system according to claim 14 , further comprising:

a second resistor connected between the output terminal of the first op-amp and the inverting terminal of the first op-amp; and

a second capacitor connected between the output terminal of the first op-amp and the inverting terminal of the first op-amp, wherein the second capacitor is connected in parallel with the second resistor.

20. The audio system according to claim 14 , further comprising:

a second resistor connected to the output terminal of the second op-amp; and

a second capacitor connected to the output terminal of the second op-amp and the non-inverting terminal of the first op-amp;

wherein the second resistor is further connected to:

the inverting terminal of the first op-amp via a third capacitor and a third resistor; and

the non-inverting terminal of the first op-amp via a fourth resistor.