Amplifier with feedback circuit

• US 10,003,312 B2
• Filed: 08/31/2015
• Issued: 06/19/2018
• Est. Priority Date: 08/31/2015
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Dhanasekaran, Vijayakumar
• Primary Examiner(s): Choe, Henry
• Application Number:
  US14/841,490
• Publication Number:
  US 20170063315A1
• Time in Patent Office: 1,023 Days
• Field of Search: 330 85, 330279, 330 95, 330 97
• CPC Class Codes: H03F 1/34 Negative-feedback-circuit arrangements with or without positive feedback H03F1/02 - H03F1/30, H03F1/38 - H03F1/50, H03F3/50 take precedence ; for rejection of common mode signals H03F3/45479
• CPC Class Codes: H03F 1/56 Modifications of input or output impedances, not otherwise provided for
• CPC Class Codes: H03F 2200/03 the amplifier being designed for audio applications
• CPC Class Codes: H03F 2200/234 the input amplifying stage being one or more operational amplifiers
• CPC Class Codes: H03F 2200/387 A circuit being added at the output of an amplifier to adapt the output impedance of the amplifier
• CPC Class Codes: H03F 2203/45136 One differential amplifier in IC-block form being shown
• CPC Class Codes: H03F 2203/45521 the FBC comprising op amp stages, e.g. cascaded stages of the dif amp and being coupled between the LC and the IC
• CPC Class Codes: H03F 2203/45522 the FBC comprising one or more potentiometers
• CPC Class Codes: H03F 2203/45528 the FBC comprising one or more passive resistors and being coupled between the LC and the IC
• CPC Class Codes: H03F 3/183 with semiconductor devices only
• CPC Class Codes: H03F 3/187 in integrated circuits
• CPC Class Codes: H03F 3/45071 with semiconductor devices only
• CPC Class Codes: H03F 3/45475 using IC blocks as the active amplifying circuit
• CPC Class Codes: H04R 2420/03 Connection circuits to selectively connect loudspeakers or headphones to amplifiers
• CPC Class Codes: H04R 2420/05 Detection of connection of loudspeakers or headphones to amplifiers
• CPC Class Codes: H04R 3/00 Circuits for transducers , loudspeakers or microphones

Abstract

An apparatus includes a resistor having an input coupled to an output of an amplifier. The apparatus also includes a feedback circuit coupled to an output of the resistor and to an input of the amplifier. The feedback circuit includes a first component of a voltage divider.

Claims

1. An apparatus comprising:

a resistor having an input and an output, the input coupled to an output of an amplifier;

a feedback circuit coupled to the output of the resistor and to an input of the amplifier, the feedback circuit comprising a first component of a voltage divider and a first feedback resistor, the first component having an input coupled to the output of the resistor and an output coupled to an input of the first feedback resistor;

a second feedback resistor coupled to the output of the amplifier and to a second input of the amplifier; and

the voltage divider including the first component, a second component, and a reference node, the first component coupled via the reference node to the second component, the reference node coupled to the output of the first component, an input of the second component, and the input of the first feedback resistor, the voltage divider configured to divide an input voltage at the input of the first component to generate a reference voltage, the reference voltage based on a product of the input voltage and a first value, the first value based on a quotient of a second resistance of the second component by a sum of a first resistance of the first component and the second resistance of the second component.

2. The apparatus of claim 1, wherein the resistor, the feedback circuit, and the second feedback resistor are included in an audio amplifier, the audio amplifier configured to connect to a headphone.

3. The apparatus of claim 1, wherein the resistor, the feedback circuit, and the second feedback resistor are included in an audio amplifier, the audio amplifier included in a wireless device.

4. The apparatus of claim 1, wherein the first component is adjustable and configured to cause an effective output resistance at the output of the resistor to dynamically match a load.

5. The apparatus of claim 1, the first component including a first resistor of the voltage divider, the second component including a second resistor of the voltage divider, and the amplifier including an operational amplifier.

6. The apparatus of claim 1, wherein a first resistance of the first feedback resistor substantially matches a second resistance of the second feedback resistor, and wherein an effective output resistance at the output of the resistor is greater than a resistance of the resistor.

7. The apparatus of claim 5, the feedback circuit further including another amplifier having an input coupled to the reference node and to the first resistor of the voltage divider and having an output coupled to the first feedback resistor.

8. The apparatus of claim 5, the feedback circuit further including a unity-gain buffer amplifier having an input coupled to the output of the resistor and having an output coupled to the first resistor of the voltage divider.

13. The apparatus of claim 1, wherein the amplifier includes an operational amplifier, wherein the first component comprises a first adjustable resistor of the voltage divider and the second component comprises a second adjustable resistor of the voltage divider, wherein an output of the second adjustable resistor is coupled to ground, wherein the second resistor is independent of the feedback circuit, and wherein a first resistance of the first feedback resistor substantially matches a second resistance of the second feedback resistor.

14. The apparatus of claim 1, wherein the resistor is coupled to and configured to provide an amplified audio signal to an output port of an audio amplifier.

15. The apparatus of claim 1, wherein the input of the amplifier and the second input of the amplifier are configured to receive a differential input signal, and wherein the input of the amplifier is configured to receive the differential input signal via a first input resistor, and wherein the second input of the amplifier is configured to receive the differential input signal via a second input resistor.

16. The apparatus of claim 1, wherein the output of the resistor and the feedback circuit are directly connected to an output port of an audio amplifier.

17. The apparatus of claim 1, further comprising the amplifier, the amplifier configured to amplify an analog audio signal, wherein the voltage divider is configured to divide, independent of current, the input voltage.

18. The apparatus of claim 1, the feedback circuit further including a second amplifier configured to amplify a feedback signal, the second amplifier coupled to first component of the voltage divider.

9. An apparatus comprising:

means for amplifying an audio signal;

means for resisting current flow, the means for resisting having an input coupled to an output of the means for amplifying;

means for biasing an input of the means for amplifying, the means for biasing including second means for resisting current flow and at least a portion of means for generating a reference voltage, the means for biasing coupled to an output of the means for resisting, the means for generating having an input coupled to the output of the means for resisting and an output coupled to an input of the second means for resisting, the second means for resisting having an output coupled to the input of the means for amplifying;

third means for resisting current flow coupled to the output of the means for amplifying and to a second input of the means for amplifying; and

the means for generating the reference voltage including fourth means for resisting current flow, fifth means for resisting current flow, and a reference node, the fourth means for resisting coupled via the reference node to the fifth means for resisting, the reference node coupled to an output of the fourth means for resisting, an input of the fifth means for resisting, and the input of the second means for resisting, the means for generating the reference voltage configured to divide an input voltage at an input of the fourth means for resisting to generate the reference voltage, the reference voltage based on a product of the input voltage and a first value, the first value based on a quotient of a second resistance of the fifth means for resisting by a sum of a first resistance of the fourth means for resisting and the fifth means for resisting.

10. The apparatus of claim 9, the means for biasing including means for modifying an effective output resistance at the output of the means for resisting.

11. The apparatus of claim 9, the means for generating coupled to the output of the means for resisting, the means for generating including means for adjusting the reference voltage.

12. A method comprising:

receiving an analog audio signal at an amplifier;

sending an output signal of the amplifier to an input of a resistor;

sending a feedback signal from an output of the resistor, via a first component of a voltage divider, a reference node of the voltage divider, and a first feedback resistor, to an input of the amplifier to cause an effective output resistance at the output of the resistor to exceed a resistance of the resistor, wherein the reference node is coupled to an output of the first component, the input of a second component of the voltage divider, and an input of the first feedback resistor, wherein the first component is coupled via the reference node to the second component, and

wherein sending the feedback single includes dividing, by the voltage divider, an output voltage of the feedback signal to generate a reference voltage based on multiplying the output voltage by a second resistance of the second component and dividing the product of the output voltage and the second resistance by a sum of a first resistance of the first component and the second resistance; and

sending a second feedback signal from an output of the amplifier via a second feedback resistor to a second input of the amplifier.