Method and apparatus for distortion reduction in a class D amplifier

• US 10,038,411 B2
• Filed: 10/31/2016
• Issued: 07/31/2018
• Est. Priority Date: 10/31/2016
• Status: Active Grant

• Current Assignee: RGB Systems Incorporated
• Original Assignee: RGB Systems Incorporated
• Inventors: Mendenhall, Eric
• Primary Examiner(s): NGUYEN, HIEU P
• Application Number:
  US15/339,387
• Publication Number:
  US 20180123527A1
• Time in Patent Office: 638 Days
• Field of Search: 330 10, 330251, 330207 A
• CPC Class Codes: H03F 1/0205 in transistor amplifiers
• CPC Class Codes: H03F 1/26 Modifications of amplifiers to reduce influence of noise generated by amplifying elements
• CPC Class Codes: H03F 1/32 Modifications of amplifiers to reduce non-linear distortion by negative feedback H03F1/34
• CPC Class Codes: H03F 2200/225 the input circuit of an amplifying stage comprising an LC-network
• CPC Class Codes: H03F 2200/459 Ripple reduction circuitry being used in an amplifying circuit
• CPC Class Codes: H03F 2201/3215 To increase the output power or efficiency
• CPC Class Codes: H03F 3/183 with semiconductor devices only
• CPC Class Codes: H03F 3/217 Class D power amplifiers; Switching amplifiers

Abstract

A Class D amplifier is described herein that includes an outer loop, an inner loop, and a notch filter. The notch filter can be located between an output of the outer loop and an input of the inner loop. Alternatively or in addition, the notch filter can be located within the outer loop of the Class D amplifier. Ripple content can initially be present at an input to the inner loop of the Class D amplifier, causing nonlinearity in the inner loop and distortion in the audio output signal. The notch filter can filter the ripple content at the input to the inner loop, thereby reducing the nonlinearity present in the inner loop and the distortion in the audio output signal.

Claims

1. An apparatus comprising:

an output;

an inner circuit loop that has an input and an output;

a filter circuit that has an input and an output, wherein the input of the filter circuit is coupled to the output of the inner circuit loop, and wherein the output of the filter circuit is coupled to the output of the apparatus;

an outer circuit loop that has an input and output, wherein the input of the outer circuit loop is coupled to the output of the filter circuit and the output of the apparatus; and

a notch filter that has an input and an output, wherein the notch filter comprises a noninverting active series LC notch filter comprising a resistor, an inductor, a capacitor, and a linear transfer function device, wherein a first end of the resistor is the input of the notch filter and is coupled to the output of the outer circuit loop, wherein a first end of the inductor is coupled in series with a first end of the capacitor, wherein a second end of the capacitor is coupled to ground, wherein a second end of the resistor and a second end of the inductor are coupled to a positive input of the linear transfer function device, wherein an output of the linear transfer function device is the output of the notch filter and is coupled to a negative input of the linear transfer function device and the input of the inner circuit loop, and wherein the notch filter is configured to reduce a portion of a ripple content originating at the output of the apparatus that is present at the input of the inner circuit loop from a first level to a second level lower than the first level.

2. The apparatus of claim 1, wherein the notch filter is configured to reduce the ripple content by 2% to 20%.

3. The apparatus of claim 1, wherein the apparatus comprises a Class D amplifier.

4. A method comprising:

generating an output signal at an output of a filter circuit and at an input of an outer circuit loop, wherein the output of the filter circuit is coupled to the input of the outer circuit loop, and wherein the output signal comprises a ripple content;

transmitting the output signal through the outer circuit loop;

filtering, via a notch filter, the ripple content present in the output signal at an output of the outer circuit loop, wherein the notch filter comprises an inverting active parallel LC notch filter comprising a first resistor, a second resistor, a third resistor, and a fourth resistor, an inductor, a capacitor, a first linear transfer function device, and a second linear transfer function device, wherein a first end of the inductor and a first end of the capacitor are coupled to the output of the outer circuit loop, wherein a second end of the inductor and a second end of the capacitor are coupled to a first end of the first resistor, wherein a second end of the first resistor is coupled to a negative input of the first linear transfer function device and a first end of the second resistor, wherein a positive input of the first linear transfer function device is coupled to ground, wherein an output of the first linear transfer function device is coupled to a second end of the second resistor and a first end of the third resistor, wherein a second end of the third resistor is coupled to a negative input of the second linear transfer function device and a first end of the fourth resistor, wherein a positive input of the second linear transfer function device is coupled to ground, and wherein an output of the second linear transfer function device is coupled to a second end of the fourth resistor and an input of an inner circuit loop; and

receiving the output signal with the filtered ripple content at the input of the an inner circuit loop, wherein an output of the inner circuit loop is coupled to an input of the filter circuit.

5. The method of claim 4, wherein filtering, via the notch filter, the ripple content present in the output signal, further comprises reducing the ripple content by 2% to 20%.

6. The method of claim 4, wherein the output voltage comprises an output voltage of a Class D amplifier.

7. A method comprising:

generating an output signal at an output of a filter circuit and at an input of an outer circuit loop, wherein the output of the filter circuit is coupled to the input of the outer circuit loop, and wherein the output signal comprises a ripple content;

transmitting the output signal through the outer circuit loop;

filtering, via a notch filter, the ripple content present in the output signal at an output of the outer circuit loop, wherein the notch filter comprises a noninverting active twin tee filter comprising a first resistor, a second resistor, a third resistor, a fourth resistor, and a fifth resistor, a first capacitor, a second capacitor, a third capacitor, a first linear transfer function device, and a second linear transfer function device, wherein a first end of the first resistor and a first end of the first capacitor are coupled to the output of the outer circuit loop, wherein a second end of the first capacitor is coupled to a first end of the third resistor and a first end of the second capacitor, wherein a second end of the first resistor is coupled to a first end of the second resistor and a first end of the third capacitor, wherein a second end of the third resistor and a second end of the third capacitor are coupled to an output of the second linear transfer function device, wherein a second end of the second resistor and a second end of the second capacitor are coupled to a positive input of the first linear transfer function device, wherein an output of the first linear transfer function device is coupled to a negative input of the first linear transfer function device, an input of an inner circuit loop, and a first end of the fourth resistor, wherein a second end of the fourth resistor is coupled to a first end of the fifth resistor and a positive input of the second linear transfer function device, wherein a second end of the fifth resistor is coupled to ground, and wherein the output of the second linear transfer function device is coupled to a negative input of the second linear transfer function device; and

receiving the output signal with the filtered ripple content at the input of the an inner circuit loop, wherein an output of the inner circuit loop is coupled to an input of the filter circuit.

8. The method of claim 7, wherein filtering, via the notch filter, the ripple content present in the output signal, further comprises reducing the ripple content by 2% to 20%.

9. The method of claim 7, wherein the output voltage comprises an output voltage of a Class D amplifier.

10. An apparatus comprising:

an output;

an inner circuit loop that has an input and an output;

a filter circuit that has an input and an output, wherein the input of the filter circuit is coupled to the output of the inner circuit loop, and wherein the output of the filter circuit is coupled to the output of the apparatus;

an outer circuit loop that has an input and output, wherein the input of the outer circuit loop is coupled to the output of the filter circuit and the output of the apparatus; and

a notch filter that has an input and an output, wherein the notch filter comprises an inverting active series LC notch filter comprising a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, an inductor, a capacitor, a first linear transfer function device, and a second linear transfer function device, wherein a first end of the first resistor is the input of the notch filter and is coupled to the output of the outer circuit loop, wherein a second end of the first resistor is coupled to a first end of the second resistor and a first end of the inductor, wherein a second end of the inductor is coupled to a first end of the capacitor, wherein a second end of the capacitor is coupled to ground, wherein a second end of the second resistor is coupled to a negative input of the first linear transfer function device and a first end of the third resistor, wherein a positive input of the first linear transfer function device is coupled to ground, wherein an output of the first linear transfer function device is coupled to a second end of the third resistor and a first end of the fourth resistor, wherein a second end of the fourth resistor is coupled to a negative input of the second linear transfer function device and a first end of the fifth resistor, wherein a positive input of the second linear transfer function device is coupled to ground, wherein an output of the second linear transfer function device is the output of the notch filter and is coupled to a second end of the fifth resistor and the input of the inner circuit loop, and wherein the notch filter is configured to reduce a portion of a ripple content originating at the output of the apparatus that is present at the input of the inner circuit loop from a first level to a second level lower than the first level.

11. The apparatus of claim 10, wherein the notch filter is configured to reduce the ripple content by 2% to 20%.

12. The apparatus of claim 10, wherein the apparatus comprises a Class D amplifier.

13. An apparatus comprising:

an output;

an inner circuit loop that has an input and an output;

a filter circuit that has an input and an output, wherein the input of the filter circuit is coupled to the output of the inner circuit loop, and wherein the output of the filter circuit is coupled to the output of the apparatus;

an outer circuit loop that has an input and output, wherein the input of the outer circuit loop is coupled to the output of the filter circuit and the output of the apparatus; and

a notch filter that has an input and an output, wherein the notch filter comprises a noninverting active parallel LC notch filter comprising a resistor, an inductor, a capacitor, and a linear transfer function device, wherein a first end of the inductor and a first end of the capacitor are the input of the notch filter and are coupled to the output of the outer circuit loop, wherein a second end of the inductor and a second end of the capacitor are coupled to a first end of the resistor and a positive input of the linear transfer function device, wherein a second end of the resistor is coupled to ground, wherein an output of the linear transfer function device is the output of the notch filter and is coupled to a negative input of the linear transfer function device and the input of the inner circuit loop, and wherein the notch filter is configured to reduce a portion of a ripple content originating at the output of the apparatus that is present at the input of the inner circuit loop from a first level to a second level lower than the first level.

14. The apparatus of claim 13, wherein the notch filter is configured to reduce the ripple content by 2% to 20%.

15. The apparatus of claim 13, wherein the apparatus comprises a Class D amplifier.