Active common mode feedback for unbalanced input and feedback signals and methods thereof

• US 6,411,165 B1
• Filed: 04/16/2001
• Issued: 06/25/2002
• Est. Priority Date: 04/17/2000
• Status: Expired due to Term

• Current Assignee: Cirrus Logic Incorporated
• Original Assignee: Tripath Technology, Inc. (Cloudward, Inc.)
• Inventors: Delano, Cary L.
• Primary Examiner(s): Shingleton, Michael B
• Application Number:
  US09/836,623
• Time in Patent Office: 435 Days
• Field of Search: 330/69, 330/85, 330/258, 330/259
• US Class Current: 330/258
• CPC Class Codes: H03F 2200/331 Sigma delta modulation being used in an amplifying circuit
• CPC Class Codes: H03F 3/45941 Controlling the input circuit of the differential amplifier

Abstract

A noise shaped differential amplifier having a reduced common mode signal in accordance with an embodiment of the invention is described. In the described embodiment, the noise shaped differential amplifier includes a noise shaper having a common mode signal controlled by an attenuation operational amplifier that is coupled to a voltage divider circuit and a sense resistor divider. In this arrangement, the attenuation operational amplifier controls a virtual ground applied to the sense resistor divider.

Claims

1. An attenuation circuit arranged to reduce a common mode potential in an amplifier having a noise shaper circuit, comprising:

a sense resistor divider;

a voltage divider circuit coupled to the sense resistor divider; and

an attenuation operational amplifier (op amp) having,

an output node connected to the voltage divider circuit,

a first input node connected to a reference voltage supply (Vref), and

a second input node connected to the sense resistor divider, wherein the attenuation op amp provides a virtual ground to a center of the sense resistor divider thereby setting a common mode potential Vcm developed at an input of the noise shaper and to reduce a common mode feedback voltage swing of the amplifier.

2. A circuit as recited in claim 1, wherein the attenuation circuit is coupled to the noise shaper having a first input node connected to a first input line and a first output line and a second input node connected to a second input line and a second output line.

3. A circuit as recited in claim 2, the sense resistor further comprises:

a first sense resistor terminal connected to the first input line and the first output line at a first node, and a second sense resistor terminal connected to the second input line and the second output line at a second node.

4. A circuit as recited in claim 3, wherein the voltage divider circuit further comprises:

a first resistor having a first resistor first terminal connected to the first node and a first resistor second terminal connected to the output node; and

a second resistor having a second resistor first terminal connected to the second node and a second resistor second terminal connected to the output node.

5. A circuit as recited in claim 4, further comprising a single ended power stage having a power stage first input coupled to the first output line and a power stage second input coupled to the second output line and a power stage output line coupled to a load.

6. A common mode potential attenuation circuit as recited in claim 5, further comprising:

a first input resistor connected in series between the first input node and the input voltage supply; and

a second input resistor connected in series between the second input node and the input power supply.

7. A method for attenuating a common mode potential by a common mode potential attenuation circuit, comprising:

providing a sense resistor divider;

providing a voltage divider circuit; and

providing an attenuation operational amplifier (op amp) having an output node, a attenuation op amp first input node, and a attenuation op amp second input node;

connecting the attenuation op amp output node to the voltage divider circuit;

connecting the attenuation op amp first input node to a reference voltage supply (V_ref), and

connecting the attenuation op amp second input node to the sense resistor divider, wherein the attenuation op amp provides a virtual ground to a center of the sense resistor divider thereby setting a common mode potential V_cm developed at an input of the noise shaper and to reduce a common mode feedback voltage swing of the amplifier.

8. A method as recited in claim 7, further comprising:

coupling the attenuation circuit to the noise shaper having a first input node connected to a first input line and a first output line and a second input node connected to a second input line and a second output line.

9. A method as recited in claim 8, further comprising:

connecting a first sense resistor terminal to the first input line and the first output line at a first node, and a second sense resistor terminal connected to the second input line and the second output line at a second node.

10. A method as recited in claim 9, further comprising:

connecting a first resistor having a first resistor first terminal to the first node and a first resistor second terminal connected to the output node; and

connecting a second resistor having a second resistor first terminal to the second node and a second resistor second terminal connected to the output node.

11. A method as recited in claim 10, further comprising:

coupling a single ended power stage having a power stage first input to the first output line and a power stage second input coupled to the second output line and a power stage output line coupled to a load.

12. A method as recited in claim 11, further comprising:

connecting a first input resistor in series between the first input node and the input voltage supply; and

connecting a second input resistor in series between the second input node and the input power supply.