US20180115285A1 - Method and circuit for suppressing pop noise in an audio operation amplifier - Google Patents

Method and circuit for suppressing pop noise in an audio operation amplifier Download PDF

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US20180115285A1
US20180115285A1 US15/347,799 US201615347799A US2018115285A1 US 20180115285 A1 US20180115285 A1 US 20180115285A1 US 201615347799 A US201615347799 A US 201615347799A US 2018115285 A1 US2018115285 A1 US 2018115285A1
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operation amplifier
audio
switch
value
audio operation
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US9954494B1 (en
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Donghui GAO
Jiazhou Liu
Dawei Guo
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Beken Corp
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Beken Corp
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
    • H03F1/26—Modifications of amplifiers to reduce influence of noise generated by amplifying elements
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
    • H03F1/30—Modifications of amplifiers to reduce influence of variations of temperature or supply voltage or other physical parameters
    • H03F1/305—Modifications of amplifiers to reduce influence of variations of temperature or supply voltage or other physical parameters in case of switching on or off of a power supply
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
    • H03F1/34—Negative-feedback-circuit arrangements with or without positive feedback
    • H03F1/342—Negative-feedback-circuit arrangements with or without positive feedback in field-effect transistor amplifiers
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/181—Low-frequency amplifiers, e.g. audio preamplifiers
    • H03F3/183—Low-frequency amplifiers, e.g. audio preamplifiers with semiconductor devices only
    • H03F3/185—Low-frequency amplifiers, e.g. audio preamplifiers with semiconductor devices only with field-effect devices
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/20—Power amplifiers, e.g. Class B amplifiers, Class C amplifiers
    • H03F3/21—Power amplifiers, e.g. Class B amplifiers, Class C amplifiers with semiconductor devices only
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/30—Single-ended push-pull [SEPP] amplifiers; Phase-splitters therefor
    • H03F3/3001—Single-ended push-pull [SEPP] amplifiers; Phase-splitters therefor with field-effect transistors
    • H03F3/3022—CMOS common source output SEPP amplifiers
    • H03F3/3028—CMOS common source output SEPP amplifiers with symmetrical driving of the end stage
    • H03F3/303—CMOS common source output SEPP amplifiers with symmetrical driving of the end stage using opamps as driving stages
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/45—Differential amplifiers
    • H03F3/45071—Differential amplifiers with semiconductor devices only
    • H03F3/45076—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier
    • H03F3/45179—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier using MOSFET transistors as the active amplifying circuit
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/45—Differential amplifiers
    • H03F3/45071—Differential amplifiers with semiconductor devices only
    • H03F3/45076—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier
    • H03F3/45179—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier using MOSFET transistors as the active amplifying circuit
    • H03F3/45183—Long tailed pairs
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
    • H03F1/02—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation
    • H03F1/0205—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation in transistor amplifiers
    • H03F1/0277—Selecting one or more amplifiers from a plurality of amplifiers
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F2200/00—Indexing scheme relating to amplifiers
    • H03F2200/03—Indexing scheme relating to amplifiers the amplifier being designed for audio applications
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F2200/00—Indexing scheme relating to amplifiers
    • H03F2200/372—Noise reduction and elimination in amplifier
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F2203/00—Indexing scheme relating to amplifiers with only discharge tubes or only semiconductor devices as amplifying elements covered by H03F3/00
    • H03F2203/30—Indexing scheme relating to single-ended push-pull [SEPP]; Phase-splitters therefor
    • H03F2203/30078—A resistor being added in the pull stage of the SEPP amplifier
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F2203/00—Indexing scheme relating to amplifiers with only discharge tubes or only semiconductor devices as amplifying elements covered by H03F3/00
    • H03F2203/30—Indexing scheme relating to single-ended push-pull [SEPP]; Phase-splitters therefor
    • H03F2203/30111—A resistor being added in the push stage of the SEPP amplifier
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F2203/00—Indexing scheme relating to amplifiers with only discharge tubes or only semiconductor devices as amplifying elements covered by H03F3/00
    • H03F2203/45—Indexing scheme relating to differential amplifiers
    • H03F2203/45151—At least one resistor being added at the input of a dif amp
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/72—Gated amplifiers, i.e. amplifiers which are rendered operative or inoperative by means of a control signal

Definitions

  • the present application relates to an audio operation amplifier and more particularly, but not exclusively, to a method and circuit for suppressing popping noise (POP noise) in an audio operation amplifier.
  • POP noise popping noise
  • a method and circuit use switches and resistors to suppress POP noise in an audio operation amplifier.
  • the method comprises: connecting a first resistor and a second resistor in series at an output stage of the audio operation amplifier by turning on a first switch and a second switch after inputting an audio signal into the audio operation amplifier; generating, with a ramp generator, a ramp voltage, wherein the ramp voltage varies from zero to a first value; generating, with an voltage generator, a second voltage, wherein a third switch is turned on and a fourth switch is turned off when the ramp voltage reaches the second value; short-circuiting the first and second resistors by turning off the first and second switches; and outputting, with the audio operation amplifier, an amplified audio signal.
  • the method comprises: connecting the first resistor and the second resistor in series at an output stage of the audio operation amplifier by turning on the first and second switches when stopping inputting the audio signal; turning off the third switch and turning on the fourth switch, wherein the ramp voltage varies from the first value to zero; and turning off the audio operation amplifier.
  • an audio device comprises: an audio operation amplifier; and a circuit in the audio operation amplifier, comprising: a first switch connected to a first resistor in parallel; a second switch connected to a second resistor in parallel; and the first resistor is configured to be connected in series to the second resistor at an output stage of the audio operation amplifier by turning on the first switch and the second switch; a ramp generator connected to the audio operation amplifier via a third switch and configured to generate a ramp voltage after an audio signal is input into the audio operation amplifier, wherein the ramp voltage varies from zero to a first value after the third switch is turned off; a voltage generator connected to the audio operation amplifier via a fourth switch and configured to generate a second voltage, wherein the third switch is turned on and the fourth switch is turned off when the ramp voltage reaches the second value, wherein the first and the second resistors are further configured to be short-circuited by turning off the first and the second switches, and the audio operation amplifier is further configured to output an amplified audio signal.
  • FIG. 1 is a diagram illustrating an embodiment of an audio device for suppressing POP noise in an audio operation amplifier according to an embodiment of the invention.
  • FIG. 2 is a diagram illustrating another embodiment of an audio device for suppressing POP noise in an audio operation amplifier according to a further embodiment of the invention.
  • FIG. 3 is a sequence diagram for a circuit for suppressing POP noise in the audio operation amplifier according to a further embodiment of the invention.
  • FIG. 4 is a flowchart of a method for suppressing POP noise in an audio operation amplifier according to an embodiment of the invention.
  • FIG. 5 is a continuation of the method illustrated in FIG. 5 .
  • FIG. 1 illustrates an embodiment of an audio device 100 including an audio operation amplifier 130 for suppressing POP noise.
  • the audio device 100 is an audio power amplifier.
  • an audio signal is input into the audio operation amplifier 130 through a resistor R 3 and the audio operation amplifier 130 is connected with a resistor R 4 in parallel.
  • a ramp generator 110 is connected to the audio operation amplifier 130 through a switch P 3 and a voltage generator 120 is connected to the audio operation amplifier 130 through a switch P 4 .
  • a capacitor C is connected between the audio operation amplifier 130 and an audio output device 140 , for example, earphone or a speaker, etc.
  • the audio output device 140 comprises a resistor R 5 .
  • the circuit in the audio operation amplifier 130 comprises two resistors R 1 and R 2 and two switches P 1 and P 2 . Wherein two resistors R 1 and R 2 are coupled at the output stage and two switches P 1 and P 2 are respectively connected to the resistors R 1 and R 2 in parallel. If the two switches P 1 and P 2 are turned on simultaneously, the two resistors R 1 and R 2 are connected in series at the output stage. If the two switches P 1 and P 2 are turned off simultaneously, the two resistors R 1 and R 2 are short-circuited.
  • the switch P 3 is turned off after the audio signal is input into the audio operation amplifier.
  • the switches P 1 and P 2 are turned on.
  • the resistors R 1 and R 2 are connected in series at the output stage of the amplifier.
  • the ramp generator generates the ramp voltage varying from 0 to a first value after the switch P 3 is turned off.
  • the switch P 4 should be turned off and then the switch P 3 should be turned on.
  • the voltage generator has generated a second voltage with a second value before the switch P 4 is turned off.
  • the second voltage generated by the voltage generator is a common-mode voltage and there is a difference between the first value and the second value.
  • the output of the audio operation amplifier 130 changes gently due to the existence of resistor R 1 and the POP noise can be reduced.
  • the difference between the first value and the second value can be controlled within 10 mv. Then, the switches P 1 and P 2 are turned off and the resistors R 1 and R 2 are short-circuited.
  • the switches P 1 and P 2 are turned on firstly. Then the resistors R 1 and R 2 are connected in series at the output stage of the amplifier. The switch P 3 is turned off and the switch P 4 is turned on. At this time, the output on Vo changes from the second value to the first value slowly. Then the ramp voltage varies from the first value to 0. During this operation, the resistor R 2 shares a part of voltage on the capacitor and the voltage on the capacitor can be reduced smoothly. Finally, the audio operation amplifier can be turned off with a smaller POP noise.
  • the output stage of the audio operation amplifier is a Class-AB output stage.
  • an audio operation amplifier 200 is a multi-stage operation amplifier that can be used in place of the amplifier 130 in the device 100 .
  • a DC level shift circuit is coupled to a circuit for suppressing POP noise and configured to shift the output stage of the audio operation amplifier.
  • the output stage 1 of the audio operation amplifier 200 and the DC level shift circuit have established the stable electric level and then the amplifier 200 can immediately stabilize after the ramp voltage reaches the first value.
  • the amplifier 200 can be closed stably.
  • the amplifier 200 can work stably during the operation being powered on and powered down and thus reduced the POP noise.
  • FIG. 3 is a sequence diagram for the audio operation amplifier 130 in the audio device 100 according to a further embodiment of the invention.
  • the switch P 3 is in a high logic level
  • the ramp voltage reaches the first value
  • the output of audio operation amplifier 130 also reaches the first value
  • the switch P 4 jumps to the high logic level, i.e., the switch P 4 is turned off.
  • the ramp voltage remains stable
  • the switch P 4 is in the high logic level
  • the switch P 3 is changing from the high logic level to the low logic level slowly.
  • the output of audio operation amplifier 130 also reaches the second value slowly.
  • the output of the audio operation amplifier 130 remains stable, the switch P 4 is in the high logic level, and the switches P 1 and P 2 jump to the high logic level, i.e., the switches P 1 and P 2 are turned off and the resistors R 1 and R 2 are short-circuited.
  • the switches P 1 and P 2 drop to the low logic level, i.e., the switches P 1 and P 2 are turned on and the resistors R 1 and R 2 are connected in series at the output stage of the amplifier 130 .
  • the switch P 3 jumps to the high logic level, the switch P 4 is in the high logic level, and the ramp voltage change from the second value to the first value slowly.
  • the output of audio operation amplifier 130 also reaches the first value slowly.
  • the switch P 4 drops to the low logic level, i.e., the voltage of the voltage generator is off and the ramp voltage start to drop from the first value to zero.
  • the output of audio operation amplifier 130 also drops from the first value to zero. It can be seen from the time sequence in FIG. 3 , the voltage change of each element in the audio operation amplifier is relatively smooth and thus the voltage change on the capacitor C in FIG. 1 can also be relatively smooth. Thus, the POP noise can be suppressed or reduced.
  • FIG. 4 is a flowchart of a method 400 for suppressing POP noise in an audio operation amplifier according to an embodiment of the invention.
  • the method 400 comprises connecting, in block 410 , a first resistor and a second resistor in series at an output stage of the audio operation amplifier by turning on a first switch and a second switch; generating, in block 420 , with a ramp generator, a ramp voltage, wherein the ramp voltage varies from zero to a first value after an audio signal is input into the audio operation amplifier; generating, in block 430 , with an voltage generator, a second voltage, wherein a third switch is turned on and a fourth switch is turned off when the ramp voltage reaches the first value; short-circuiting, in block 440 , the first and the second resistors by turning off the first and the second switches; and outputting, in block 450 , with the audio operation amplifier, an amplified audio signal.
  • FIG. 5 is a continuation of the method 400 illustrated in FIG. 4 .
  • the method 400 further comprises connecting, in block 510 , the first resistor and the second resistor in series at an output stage of the audio operation amplifier by turning on the first and the second switches when stopping inputting the audio signal; turning off, in block 520 , the third switch and turning on the fourth switch, wherein the ramp voltage varies from the first value to zero; and turning off, in block 530 , the audio power amplifier.
  • the second voltage is a common-mode voltage and a difference between value of the first voltage and the second value is smaller than a value.
  • the value is 10 mV.
  • the output stage of the audio operation amplifier is a Class-AB output stage.
  • the audio operation amplifier is a multi-stage operation amplifier.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Multimedia (AREA)
  • Amplifiers (AREA)

Abstract

A method for suppressing POP noise in an audio operation amplifier, comprising: connecting a first resistor and a second resistor in series at an output stage of the audio operation amplifier by turning on a first switch and a second switch; generating, with a ramp generator, a ramp voltage after an audio signal is input into the audio operation amplifier, wherein the ramp voltage varies from zero to a first value; generating, with an voltage generator, a second voltage, wherein a third switch is turned on and a fourth switch is turned off when the ramp voltage reaches the second value; short-circuiting the first and second resistors by turning off the first and second switches; and outputting, with the audio operation amplifier, an amplified audio signal.

Description

    CLAIM OF PRIORITY
  • This application claims priority to Chinese Application number 201610949358.8, entitled “A METHOD AND CIRCUIT FOR SUPPRESSING POP NOISE IN AN AUDIO OPERATION AMPLIFIER,” filed on Oct. 26, 2016 by Beken Corporation, which is incorporated herein by reference.
    • TECHNICAL FIELD
  • The present application relates to an audio operation amplifier and more particularly, but not exclusively, to a method and circuit for suppressing popping noise (POP noise) in an audio operation amplifier.
    • BACKGROUND OF THE INVENTION
  • In an audio operation amplifier, there is POP noise produced when an audio power amplifier is switched on or off. This POP noise is annoying to users and may hurt electronic components in the audio operation amplifier.
  • Conventionally, to eliminate the POP noise, additional components in the amplifier are utilized, such as multiple large capacitors and multiple external contacts. However, these additional components use valuable real estate and increase cost and complexity of the amplifier.
  • As a result, a new method and circuit for suppressing POP noise in an audio operation amplifier may be necessary.
    • BRIEF DESCRIPTION OF THE INVENTION
  • According to an embodiment of the invention, a method and circuit use switches and resistors to suppress POP noise in an audio operation amplifier.
  • In an embodiment, the method comprises: connecting a first resistor and a second resistor in series at an output stage of the audio operation amplifier by turning on a first switch and a second switch after inputting an audio signal into the audio operation amplifier; generating, with a ramp generator, a ramp voltage, wherein the ramp voltage varies from zero to a first value; generating, with an voltage generator, a second voltage, wherein a third switch is turned on and a fourth switch is turned off when the ramp voltage reaches the second value; short-circuiting the first and second resistors by turning off the first and second switches; and outputting, with the audio operation amplifier, an amplified audio signal.
  • In another embodiment, the method comprises: connecting the first resistor and the second resistor in series at an output stage of the audio operation amplifier by turning on the first and second switches when stopping inputting the audio signal; turning off the third switch and turning on the fourth switch, wherein the ramp voltage varies from the first value to zero; and turning off the audio operation amplifier.
  • In still another embodiment, an audio device comprises: an audio operation amplifier; and a circuit in the audio operation amplifier, comprising: a first switch connected to a first resistor in parallel; a second switch connected to a second resistor in parallel; and the first resistor is configured to be connected in series to the second resistor at an output stage of the audio operation amplifier by turning on the first switch and the second switch; a ramp generator connected to the audio operation amplifier via a third switch and configured to generate a ramp voltage after an audio signal is input into the audio operation amplifier, wherein the ramp voltage varies from zero to a first value after the third switch is turned off; a voltage generator connected to the audio operation amplifier via a fourth switch and configured to generate a second voltage, wherein the third switch is turned on and the fourth switch is turned off when the ramp voltage reaches the second value, wherein the first and the second resistors are further configured to be short-circuited by turning off the first and the second switches, and the audio operation amplifier is further configured to output an amplified audio signal.
    • BRIEF DESCRIPTION OF THE DRAWINGS
  • Non-limiting and non-exhaustive embodiments of the present invention are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified.
  • FIG. 1 is a diagram illustrating an embodiment of an audio device for suppressing POP noise in an audio operation amplifier according to an embodiment of the invention.
  • FIG. 2 is a diagram illustrating another embodiment of an audio device for suppressing POP noise in an audio operation amplifier according to a further embodiment of the invention.
  • FIG. 3 is a sequence diagram for a circuit for suppressing POP noise in the audio operation amplifier according to a further embodiment of the invention.
  • FIG. 4 is a flowchart of a method for suppressing POP noise in an audio operation amplifier according to an embodiment of the invention.
  • FIG. 5 is a continuation of the method illustrated in FIG. 5.
    •  DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
  • Various aspects and examples of the invention will now be described. The following description provides specific details for a thorough understanding and enabling description of these examples. Those skilled in the art will understand, however, that the invention may be practiced without many of these details. Additionally, some well-known structures or functions may not be shown or described in detail, so as to avoid unnecessarily obscuring the relevant description.
  • The terminology used in the description presented below is intended to be interpreted in its broadest reasonable manner, even though it is being used in conjunction with a detailed description of certain specific examples of the invention. Certain terms may even be emphasized below, however, any terminology intended to be interpreted in any restricted manner will be overtly and specifically defined as such in this Detailed Description section.
  • Now referring to FIG. 1, FIG. 1 illustrates an embodiment of an audio device 100 including an audio operation amplifier 130 for suppressing POP noise. The audio device 100 is an audio power amplifier. In the device 100, an audio signal is input into the audio operation amplifier 130 through a resistor R3 and the audio operation amplifier 130 is connected with a resistor R4 in parallel. A ramp generator 110 is connected to the audio operation amplifier 130 through a switch P3 and a voltage generator 120 is connected to the audio operation amplifier 130 through a switch P4. A capacitor C is connected between the audio operation amplifier 130 and an audio output device 140, for example, earphone or a speaker, etc. The audio output device 140 comprises a resistor R5. For example, the value of the resistor R5 in the earphone is about 16 ohm and the value of the resistor R5 in the speaker is about 600 ohm. Further, as shown in FIG. 1, the circuit in the audio operation amplifier 130 comprises two resistors R1 and R2 and two switches P1 and P2. Wherein two resistors R1 and R2 are coupled at the output stage and two switches P1 and P2 are respectively connected to the resistors R1 and R2 in parallel. If the two switches P1 and P2 are turned on simultaneously, the two resistors R1 and R2 are connected in series at the output stage. If the two switches P1 and P2 are turned off simultaneously, the two resistors R1 and R2 are short-circuited. In one embodiment, during the operation for powering on the audio power amplifier, the switch P3 is turned off after the audio signal is input into the audio operation amplifier. The switches P1 and P2 are turned on. Thus the resistors R1 and R2 are connected in series at the output stage of the amplifier. Then the ramp generator generates the ramp voltage varying from 0 to a first value after the switch P3 is turned off. When the ramp voltage reaches the first value, the switch P4 should be turned off and then the switch P3 should be turned on. The voltage generator has generated a second voltage with a second value before the switch P4 is turned off. In one embodiment, the second voltage generated by the voltage generator is a common-mode voltage and there is a difference between the first value and the second value. In the embodiment, during the voltage changes from the first value to the second value, the output of the audio operation amplifier 130 changes gently due to the existence of resistor R1 and the POP noise can be reduced. In the embodiment, the difference between the first value and the second value can be controlled within 10 mv. Then, the switches P1 and P2 are turned off and the resistors R1 and R2 are short-circuited.
  • During the operation for powering off the audio power amplifier, the switches P1 and P2 are turned on firstly. Then the resistors R1 and R2 are connected in series at the output stage of the amplifier. The switch P3 is turned off and the switch P4 is turned on. At this time, the output on Vo changes from the second value to the first value slowly. Then the ramp voltage varies from the first value to 0. During this operation, the resistor R2 shares a part of voltage on the capacitor and the voltage on the capacitor can be reduced smoothly. Finally, the audio operation amplifier can be turned off with a smaller POP noise.
  • Alternatively, the output stage of the audio operation amplifier is a Class-AB output stage.
  • In a further embodiment, as shown in FIG. 2, an audio operation amplifier 200 is a multi-stage operation amplifier that can be used in place of the amplifier 130 in the device 100. Wherein, a DC level shift circuit is coupled to a circuit for suppressing POP noise and configured to shift the output stage of the audio operation amplifier. In the embodiment, during the operation for powering on the audio power amplifier, in the process of generating the ramp voltage with a value from 0 to a first value, the output stage 1 of the audio operation amplifier 200 and the DC level shift circuit have established the stable electric level and then the amplifier 200 can immediately stabilize after the ramp voltage reaches the first value. During the operation for powering off the audio power amplifier, the electric level of the output stage 1 and the DC level shift circuit remain stable in the process of the ramp voltage changes from the first value to 0, and after the ramp voltage change is over, the amplifier 200 can be closed stably. Thus, the amplifier 200 can work stably during the operation being powered on and powered down and thus reduced the POP noise.
  • FIG. 3 is a sequence diagram for the audio operation amplifier 130 in the audio device 100 according to a further embodiment of the invention. In one embodiment, during the operation for powering on the audio operation amplifier 130, at time t1, the switch P3 is in a high logic level, the ramp voltage reaches the first value, the output of audio operation amplifier 130 also reaches the first value, and the switch P4 jumps to the high logic level, i.e., the switch P4 is turned off. At time t2, the ramp voltage remains stable, the switch P4 is in the high logic level, and the switch P3 is changing from the high logic level to the low logic level slowly. The output of audio operation amplifier 130 also reaches the second value slowly. At time t3, the output of the audio operation amplifier 130 remains stable, the switch P4 is in the high logic level, and the switches P1 and P2 jump to the high logic level, i.e., the switches P1 and P2 are turned off and the resistors R1 and R2 are short-circuited. In another embodiment, during the operation for powering off the audio operation amplifier 130, at time t4, the switches P1 and P2 drop to the low logic level, i.e., the switches P1 and P2 are turned on and the resistors R1 and R2 are connected in series at the output stage of the amplifier 130. At time t5, the switch P3 jumps to the high logic level, the switch P4 is in the high logic level, and the ramp voltage change from the second value to the first value slowly. The output of audio operation amplifier 130 also reaches the first value slowly. At time t6, the switch P4 drops to the low logic level, i.e., the voltage of the voltage generator is off and the ramp voltage start to drop from the first value to zero. The output of audio operation amplifier 130 also drops from the first value to zero. It can be seen from the time sequence in FIG. 3, the voltage change of each element in the audio operation amplifier is relatively smooth and thus the voltage change on the capacitor C in FIG. 1 can also be relatively smooth. Thus, the POP noise can be suppressed or reduced.
  • FIG. 4 is a flowchart of a method 400 for suppressing POP noise in an audio operation amplifier according to an embodiment of the invention. The method 400 comprises connecting, in block 410, a first resistor and a second resistor in series at an output stage of the audio operation amplifier by turning on a first switch and a second switch; generating, in block 420, with a ramp generator, a ramp voltage, wherein the ramp voltage varies from zero to a first value after an audio signal is input into the audio operation amplifier; generating, in block 430, with an voltage generator, a second voltage, wherein a third switch is turned on and a fourth switch is turned off when the ramp voltage reaches the first value; short-circuiting, in block 440, the first and the second resistors by turning off the first and the second switches; and outputting, in block 450, with the audio operation amplifier, an amplified audio signal.
  • FIG. 5 is a continuation of the method 400 illustrated in FIG. 4. As shown in FIG. 5, the method 400 further comprises connecting, in block 510, the first resistor and the second resistor in series at an output stage of the audio operation amplifier by turning on the first and the second switches when stopping inputting the audio signal; turning off, in block 520, the third switch and turning on the fourth switch, wherein the ramp voltage varies from the first value to zero; and turning off, in block 530, the audio power amplifier.
  • Alternatively, the second voltage is a common-mode voltage and a difference between value of the first voltage and the second value is smaller than a value. For example, the value is 10 mV.
  • Alternatively, the output stage of the audio operation amplifier is a Class-AB output stage.
  • Alternatively, the audio operation amplifier is a multi-stage operation amplifier.
  • This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural components that do not differ from the literal language of the claims, or if they include equivalent structural components with insubstantial differences from the literal languages of the claims.

Claims (12)

1. An audio device, comprising:
an audio operation amplifier; and
a circuit for suppressing POP noise in the audio operation amplifier, comprising:
a first switch connected to a first resistor in parallel;
a second switch connected to a second resistor in parallel; and
the first resistor is configured to be connected in series to the second resistor at an output stage of the audio operation amplifier by turning on the first switch and the second switch simultaneously;
a ramp generator connected to the audio operation amplifier via a third switch and configured to generate a ramp voltage after an audio signal is input into the audio operation amplifier, wherein the ramp voltage varies from zero to a first value after the third switch is turned off;
a voltage generator connected to the audio operation amplifier via a fourth switch and configured to generate a second voltage, wherein the third switch is turned on and the fourth switch is turned off when the ramp voltage reaches a second value,
wherein the first and the second resistors further configured to be short-circuited by turning off the first and the second switches simultaneously, and the audio operation amplifier is further configured to output an amplified audio signal.
2. The audio device of claim 1, wherein the first and the second resistors further configured to be connected in series at the output stage of the audio operation amplifier by turning on the first and the second switches when stopping inputting the audio signal, wherein the output of the audio operation amplifier changes from second to first value slowly;
the ramp voltage varies from the first value to zero after the third switch is turned off and the fourth switch is turned on; and
the audio operation amplifier further configured to be turned off.
3. The audio device of claim 1, wherein the second voltage is a common-mode voltage.
4. The audio device of claim 3, wherein a difference between value of the first value and the second value is smaller than 10 mV.
5. The audio device of claim 2, wherein the output stage of the audio operation amplifier is a Class-AB output stage.
6. The audio device of claim 2, wherein the audio operation amplifier is a multi-stage operation amplifier.
7. A method for suppressing POP noise in an audio operation amplifier, comprising:
connecting a first resistor and a second resistor in series at an output stage of the audio operation amplifier by turning on a first switch and a second switch simultaneously;
generating, with a ramp generator, a ramp voltage after an audio signal is input into the audio operation amplifier, wherein the ramp voltage varies from zero to a first value;
generating, with a voltage generator, a second voltage, wherein a third switch is turned on and a fourth switch is turned off when the ramp voltage reaches a second value;
short-circuiting the first and the second resistors by turning off the first and the second switches simultaneously; and
outputting, with the audio operation amplifier, an amplified audio signal.
8. The method of claim 7, further comprising:
connecting the first resistor and the second resistor in series at an output stage of the audio operation amplifier by turning on the first and the second switches when stopping inputting the audio signal;
turning off the third switch and turning on the fourth switch, wherein the ramp voltage varies from the first value to zero; and
turning off the audio operation amplifier.
9. The method of claim 7, wherein the second voltage is a common-mode voltage.
10. The method of claim 9, wherein a difference between value of the first value and the second value is smaller than 10 mV.
11. The method of claim 8, wherein the output stage of the audio operation amplifier is a Class-AB output stage.
12. The method of claim 8, wherein the audio operation amplifier is a multi-stage operation amplifier.
US15/347,799 2016-10-26 2016-11-10 Method and circuit for suppressing pop noise in an audio operation amplifier Active US9954494B1 (en)

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