Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
  • G01R19/165—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values
  • G01R19/16566—Circuits and arrangements for comparing voltage or current with one or several thresholds and for indicating the result not covered by subgroups G01R19/16504, G01R19/16528, G01R19/16533
  • G01R19/16571—Circuits and arrangements for comparing voltage or current with one or several thresholds and for indicating the result not covered by subgroups G01R19/16504, G01R19/16528, G01R19/16533 comparing AC or DC current with one threshold, e.g. load current, over-current, surge current or fault current
• • 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
  • H03F3/217—Class D power amplifiers; Switching amplifiers
  • H03F3/2173—Class D power amplifiers; Switching amplifiers of the bridge type
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
  • H02H9/00—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection
  • H02H9/02—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection responsive to excess current
  • H02H9/025—Current limitation using field effect transistors
• • 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
  • H03F3/217—Class D power amplifiers; Switching amplifiers
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R3/00—Circuits for transducers, loudspeakers or microphones
  • H04R3/007—Protection circuits for transducers
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11C—STATIC STORES
  • G11C27/00—Electric analogue stores, e.g. for storing instantaneous values
  • G11C27/02—Sample-and-hold arrangements
  • G11C27/024—Sample-and-hold arrangements using a capacitive memory element
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R2499/00—Aspects covered by H04R or H04S not otherwise provided for in their subgroups
  • H04R2499/10—General applications
  • H04R2499/11—Transducers incorporated or for use in hand-held devices, e.g. mobile phones, PDA's, camera's

Definitions

• the present disclosure in accordance with one or more embodiments, relates generally to signal processing and, more particularly for example, to sensing a current at an output of a switching amplifier.
• a switching amplifier may provide twenty watts of power to amplify an audio signal and drive a speaker. Due to limitations of miniature speakers used in such devices, the current to the speakers may be measured to aid in the prevention of distortion, physical damage to the speaker and other unwanted effects. Thus, there is a continued need to improve the measurement of current provided to the speaker by the switching amplifier to protect the speaker from distortion or damage.
• FIG. 1 illustrates an exemplary audio codec in accordance with one or more embodiments of the disclosure.
• FIG. 2 illustrates a schematic diagram of an exemplary audio amplifier output driver in accordance with one or more embodiments of the disclosure.
• FIG. 3 illustrates exemplary plots of control voltages and sensed current of an audio amplifier output driver in accordance with an embodiment of the disclosure.
• FIG. 4 illustrates a schematic diagram of an exemplary audio amplifier output driver including a sample and hold circuit in accordance with one or more embodiments of the disclosure.
• FIG. 5 illustrates an exemplary process flow for an audio amplifier output driver speaker protection system in accordance with one or more embodiments of the disclosure.
• an audio system of the present disclosure includes a switching amplifier H-bridge output stage, and one or more output current measurement circuits.
• Each output current measurement circuit includes a current sensing component, such as a current mirror circuit, and a shielding switch arranged to provide for accurate measurement of the current traveling through a load during all phases of amplifier switching including switching amplifier output state transitions.
• Embodiments of the present disclosure may be contrasted to pre-existing solutions for measuring a current at an output of a switching regulator or class-D switching amplifier.
• conventional switching amplifier current sensing circuits may use a sense resistor installed in series with a load to sense a current traveling through the load.
• a sensing amplifier connected to the sensing resistor may require a relatively large common mode rejection ratio to process large switching amplifier output voltage variations at the sense resistor.
• Many passive current sense circuits reduce efficiencies in the operation of an H- bridge amplifier output stage through additional power dissipation losses within the system.
• added power dissipation may cause thermal issues for applications that include switching amplifier circuits formed within an integrated circuit die.
• Some conventional audio systems use a current mirror circuit for load current sensing measurements.
• performance of current mirror circuits may be affected by similar common mode limitations as discussed herein.
• a conventional current mirror circuit used with switching amplifier applications may be subject to large voltage swings, requiring a current mirror circuit with a relatively high common mode rejection ratio.
• the current mirror circuit does not provide an accurate current measurement when switching transistors are in transition between "on" and "off states.
• Various embodiments of the present disclosure address these issues to accurately and effectively measure the current provided to the load by a switching amplifier to protect the load, such as a speaker, from distortion or damage.
• FIG. 1 illustrates a block diagram of an exemplary audio codec circuit 100 in accordance with one or more embodiments of the disclosure.
• Audio codec circuit 100 provides analog and digital circuitry for signal processing of audio inputs.
• Audio codec circuit 100 includes circuitry to process input digital signals and provide amplified output signals to a speaker, for output device 121.
• audio codec circuit 100 receives digital signals at input ports 105A-B.
• Digital signals may be provided, for example, by any electronic device such as a laptop computer, a computer tablet, a smart phone, or a sensor such as a microphone.
• Digital-to-analog converter (DAC) 107 may be configured to receive digital signals and convert the digital signals to analog signals for further processing.
• Control circuit 109 receives analog audio signals from DAC 107 and processes the analog audio signals.
• control circuit 109 provides pulse width modulated signals to audio amplifier 108.
• audio amplifier 108 is implemented as a class-D switching amplifier and pulse width modulated signals control a switching duty cycle of audio amplifier 108.
• Audio amplifier 108 amplifies the received analog audio signals and provides amplified audio signals 131A-B to drive an output device 121 at output jacks 119A-B.
• Output device 121 may be a loudspeaker, headphones or another electronic device for receiving the amplified audio signals 131A-B.
• Audio amplifier 108 is electrically coupled to current measurement circuit 110.
• Current measurement circuit 110 is configured to sense the current signal traveling to output device 121 at a low side output switch of audio amplifier 108.
• current measurement circuit 110 provides an approximation of the current of the current signal traveling through output device 121.
• a current mirror circuit within current measurement circuit 110 provides for and measures the equivalent current.
• a measured current signal 120 is provided to an overcurrent protection circuit 117.
• overcurrent protection circuit 117 adjusts a frequency of the pulse width modulated signals to reduce a magnitude of the current traveling to output device 121, if measured current signal 120 exceeds an upper current threshold.
• the upper current threshold may be the maximum current an output device 121 can withstand without distortion or physical damage and may be dependent on the materials and processes used to manufacture output device 121. For example, a miniature speaker used in modern electronic devices may be capable to withstand approximately five hundred milliampere steady state.
• overcurrent protection circuit 117 provides an overcurrent control signal 118 to turn off audio amplifier 108 if the measured current signal 120 exceeds the upper current threshold.
• Current measurement circuit 110 is operable to provide an equivalent current of the instantaneous current traveling to output device 121 while the low side output switch is active.
• Current measurement circuit 110 is also operable to provide an equivalent current of the load current when the low side output switch and the high side output switch are transitioning between an "on" and "off state.
• current measurement circuit 110 and overcurrent protection circuit 117 robustly protect output device 121 from instantaneous distortion or physical damage by comparing the measured current signal 120 to the upper current threshold and acting to adjust a current in response to the threshold being exceeded.
• Current measurement circuit 110 may also provide an analog voltage equivalent of measured current signal 120 to a speaker protection circuit 111.
• an analog-to-digital converter (ADC) 113 converts the analog voltage to a digital voltage signal 122 that represents the measured current signal 120.
• ADC 113 provides the digital voltage signal 122 to the speaker protection circuit 111 which further processes the digital voltage signal 122.
• speaker protection circuit 111 provides DAC 107 with signals 114 to adjust DAC 107 signal processing based on measured current feedback to protect the output device 121 (e.g., a speaker).
• FIG. 2 illustrates a schematic diagram of an exemplary audio amplifier output driver 200 in accordance with an embodiment of the disclosure.
• audio amplifier output driver 200 forms part of audio amplifier 108 that is implemented in audio codec circuit 100. Audio amplifier output driver 200 provides an audio output to drive a speaker load 235, which may be implemented in a mobile phone, laptop computer, tablet, audio/video system, or other similar device. In various embodiments, audio amplifier output driver 200 is implemented as a class-D amplifier, H-bridge output stage 201. Audio amplifier output driver 200 is coupled to one or more current measurement circuits 210.
• H-bridge output stage 201 includes four n-channel laterally diffused metal oxide semiconductor field-effect transistors (MOSFET) Ml, M2, M3, and M4.
• MOSFET metal oxide semiconductor field-effect transistors
• the respective drains of the first two high side transistors M3, M4 are connected to a supply voltage Pvdd.
• supply voltage Pvdd provides twelve volts DC power to transistors M3, M4.
• other power supply voltages may be provided in other embodiments.
• the respective sources are connected to drains of two low side transistors Ml, M2 whose sources are connected to ground signal 221.
• a speaker load 235 is connected between transistor switch pairs M3, Ml and M4, M2. Control circuit 109 of FIG.
• a first pulse width modulated (PMW) control signal 202 is connected to a gate terminal of transistor M3, a second PMW control signal 202 is connected to a gate terminal of transistor Ml, a third PMW control signal 202 is connected to a gate terminal of transistor M4, and a fourth PMW control signal 202 is connected to a gate terminal of transistor M2.
• PMW pulse width modulated
• a first current measurement circuit 210 includes a current mirror amplifier 211 (e.g., a current sensing circuit), n-channel MOS transistors SI and S2, a shielding switch 224, and a pull-down resistor 225.
• a current mirror amplifier 211 e.g., a current sensing circuit
• n-channel MOS transistors SI and S2 n-channel MOS transistors SI and S2
• shielding switch 224 e.g., a shielding switch
• a pull-down resistor 225 e.g., the current Ispk traveling through speaker load 235 is represented by an equivalent measured current Isensep and Isensen.
• Current mirror amplifier 211 includes two input terminals, non-inverting input terminal 212 and inverting input terminal 214.
• Non-inverting input terminal 212 is connected to a source terminal of shielding switch 224.
• a drain terminal of shielding switch 224 is connected to source terminal of transistor M3 (e.g., a first transistor switch) and drain terminal of transistor Ml (e.g., a second transistor switch).
• Inverting input terminal 214 of current mirror amplifier 211 is connected to source terminal of transistor SI and drain terminal of transistor S2.
• Current mirror amplifier 211 output signal 216 is connected to gate terminal of transistor SI to drive transistor SI.
• Source terminal of transistor S2 is connected to ground signal 221. Drain terminal of transistor SI is connected to Isensep current signal.
• Shielding switch 224 gate terminal is connected to gate terminal of low side transistor Ml. As second PWM control signal 202 turns on transistor Ml, shielding switch
• Node Va is connected to non-inverting input terminal of 212 of current mirror amplifier 211 to provide voltage Va to current mirror amplifier 211.
• Current mirror amplifier 211 output signal 216 controls a gate voltage of SI to adjust a drain-source voltage across S2.
• the voltage across transistor Ml, and equivalently at node Va is mirrored across transistor SI to provide a Isensep current signal flowing through switches SI and S2 that is approximately equal to load current Ispk.
• current mirror amplifier 211 is implemented as a laterally diffused metal oxide semiconductor circuit. Pull-down resistor
• node Va e.g., at source terminal of shielding switch 2214
• ground signal 221 to provide for a fast transition to zero volts at node Va when shielding switch 224 is turned off.
• a complementary second current measurement circuit 210B includes a current mirror amplifier 21 IB, n-channel MOS transistors S3 and S4, a shielding switch 224B, and a pull-down resistor 225B.
• Current Ispk traveling through speaker load 235 at the H-bridge complementary transistor pair (e.g., M4 and M2) is represented by an equivalent measured current Isensen.
• Current mirror amplifier 21 IB includes two input terminals, non-inverting input terminal 215 and inverting input terminal 217.
• Non- inverting input terminal 215 is connected to a source terminal of shielding switch 224B.
• a drain terminal of shielding switch 224B is connected to source terminal of transistor M4 (e.g., a third transistor switch) and drain terminal of transistor M2 (e.g., a fourth transistor switch).
• Inverting input terminal 217 of current mirror amplifier 21 IB is connected to source terminal of transistor S3 and drain terminal of transistor S4.
• Current mirror amplifier 21 IB output signal 219 is connected to gate terminal of transistor S3 to drive transistor S3.
• Source terminal of transistor S4 is connected to ground signal 221.
• Drain terminal of transistor SI is connected to Isensen current signal.
• Shielding switch 224B gate terminal is connected to gate terminal of low side transistor M2. As fourth PWM control signal 202 turns on transistor M2, shielding switch 224B turns on in response to fourth PWM control signal 202 and provides a small signal DC voltage of approximately fifty millivolts at node Vab connected to source terminal of shielding switch 224B. Node Va is connected to non-inverting input terminal of 215 of current mirror amplifier 21 IB to provide voltage Va to current mirror amplifier 21 IB.
• Current mirror amplifier 21 IB output signal 219 controls a gate voltage of S3 to control a drain-source voltage at S4 and provide current Isensen that mirrors load current Ispk.
• Pulldown resistor 225B is connected between node Vab and ground signal 221 to provide for a fast transition to zero volts at node Vab when shielding switch 224b is turned off.
• Power supply Avdd is connected to gates of transistors S2 and S4 to turn on transistor S2 and S4 when audio amplifier output driver 200 is powered on.
• transistors S2 and S4 mirror the current flowing in speaker load 235, as discussed herein.
• Speaker load 235 is connected between source of M3 and drain of Ml on a first end and source of M4 and drain of M2 on a second end.
• Transistor S2 mirrors a current flowing through transistor Ml (e.g., a second transistor switch) during the PWM cycles when Ml is conducting.
• Transistor S4 mirrors a current flowing through transistor M2 (e.g., a fourth transistor switch) during the PWM cycles that M2 is conducting.
• a speaker load 235 current is sensed for the complete range of Ispk current when Ispk flows through combined transistors Ml and M2.
• FIG. 3 illustrates plots of control voltages and sensed current of an audio amplifier output driver in accordance with an embodiment of the disclosure.
• FIG. 3 shows a plot 305 of gate voltage, Vgate, at gate terminals of transistor switch Ml and shielding switch 224 during a first transition 340 and a second transition 340B.
• first transition 340 illustrates Vgate transitioning from zero volts to five volts.
• Second transition 340B illustrates Vgate transitioning from five volts to zero volts.
• transistor switch M3 e.g., first transistor switch
• transistor switch Ml e.g., second transistor switch
• transistor switch M3 e.g., first transistor switch
• transistor switch Ml e.g., second transistor switch
• Second PWM control signal 202 controls turning on and turning off of transistor switch Ml and shielding switch 224.
• Fourth PWM control signal 202 controls turning on and turning off of transistor switch M2 and shielding switch 224B.
• Plot 310 illustrates a voltage, Vout, at source terminal M3 and drain terminal Ml during the same transitions of plot 305.
• Plot 310 shows Vout transitioning from twelve volts (e.g., Pvdd) to zero volts caused by PWM control signal 202 turning off transistor switch M3 and turning on transistor switch Ml.
• Pvdd twelve volts
• the voltage at Vgate moves from zero volts to approximately 1.3 volts and finally to five volts during this same first transition 340.
• Plot 315 illustrates node voltage Va during the same transitions 340 and 340B.
• Va is a steady fifty millivolts during all transitions and including a transistor switch Ml "on" time during transition 341.
• shielding switch 224 provides a small signal voltage (e.g., fifty millivolts) at non-inverting input terminal of current mirror amplifier 211 during transitions 340, 341, and 340B unaffected by voltage transitions of Vout and Vgate.
• current measurement circuit 210 provides a measured Isensep value that is accurate and stable during transitions 340, 341, and 340B.
• FIG. 4 illustrates a schematic diagram of an exemplary audio amplifier output driver 200 including a sample and hold circuit 425 in accordance with an embodiment of the disclosure.
• Sample and hold circuit 425 is arranged to receive the small DC signal voltage (e.g., such as small signal DC voltage of approximately fifty millivolts) from the source of shielding switch 224 and provide the small DC signal voltage to the current mirror amplifier 211 for a pre-determined sample time period.
• sample and hold circuit 425 is coupled between source terminal of shielding switch 224 and non-inverting input terminal 212 of current mirror amplifier 211.
• sample and hold circuit 425 is implemented as a capacitor, field effect transistor switch and an operational amplifier.
• the operational amplifier charges or discharges the capacitor to approximately the voltage level at the input, such as the small signal voltage.
• the charged voltage is switched to an output of sample and hold circuit 425 and provided to non- inverting input terminal 212 of current mirror amplifier 211 for the pre-determined sample time period.
• Sample and hold circuit 425 includes a trigger circuit 420 configured to provide the small signal voltage to the current mirror amplifier 211 in response to second modulated pulse control signal 202.
• sample and hold circuit 425 is operable to provide the small signal voltage for a time equal to second modulated pulse control signal 202 time period.
• the small signal voltage is provided to current mirror amplifier 211 for a time less than the time period of the second modulated pulse control signal 202.
• sample and hold circuit 425 holds the small signal voltage at the current mirror amplifier 211 to enable measurement of current Isensep (e.g., or Isensen for the complementary circuit) for a pre-determined sample time period.
• Second current measurement circuit 210B includes a second sample and hold circuit 425B and its corresponding trigger circuit 420B connected between shielding switch 224B and current mirror amplifier 21 IB to perform the sample and hold function described herein.
• FIG. 5 illustrates an exemplary process flow for an audio amplifier output driver speaker protection system in accordance with an embodiment of the disclosure.
• Audio amplifier output driver 200 includes an H-bridge output stage 201 including two high side/low side output transistor switch pairs, each pair connected to a respective end of speaker load 235 to conduct a current through speaker load 235.
• each high side transistor switch is connected to a twelve volt DC power supply and each low side transistor switch is connected to ground signal 221 to drive speaker load 235.
• a first pulse width modulated control signal is coupled to a gate terminal of a first transistor switch (e.g., high side switch M3) to control an "on" and “off state of the first transistor switch.
• a second pulse width modulated control signal is coupled to a gate terminal of a second transistor switch (e.g., low side switch Ml) to control an "on" and “off” state of the second transistor switch.
• H-bridge output stage 201 includes a complementary high side/low side transistor switch pair (e.g., M4/M2) connected to a second end of speaker load 235 and are controlled by complementary pulse width modulated control signals 202.
• shielding switch 224 provides a small signal DC voltage (e.g., approximately fifty millivolts) at non-inverting input terminal of current mirror amplifier 211 to provide the small signal DC voltage at current mirror amplifier 211 non-inverting input terminal 212 during transitions between "off and "on” states of the first and second switching transistors, and "on" state of second transistor switch (e.g., low side transistor switch).
• shielding switch 224 provides a small signal voltage (e.g., fifty millivolts) unaffected by switching voltage transitions of transistor switches.
• H-bridge output stage 201 includes a complementary second current measurement circuit 210B configured to sense the equivalent speaker current Isensen at the complementary high side/low side switch pair. In this regard, a speaker load 235 current is sensed for the complete range of speaker current comprising Isensep and Isensen.
• current measurement circuit 210 provides the measured currents Isensep and Isensen to an overcurrent protection circuit 117.
• overcurrent protection circuit 117 may adjust a frequency of the first and second pulse width modulated control signals to reduce the current traveling through the speaker load 235 when speaker current Ispk exceeds an upper current threshold.
• current measurement circuit 210 may provide analog voltage signals of measured currents Isensep and Isensen to an ADC 113 for conversion to digital sense signals that are passed to a speaker protection circuit 111.
• Speaker protection circuit 111 may process the digital sense signals and provide gain adjustments to DAC 107 to adjust a speaker load 235 current at outputs of audio amplifier output driver 200.
• various embodiments provided by the present disclosure may be implemented using hardware, software, or combinations of hardware and software.
• the various hardware components and/or software components set forth herein may be combined into composite components comprising software, hardware, and/or both without departing from the spirit of the present disclosure.
• the various hardware components and/or software components set forth herein may be separated into sub-components comprising software, hardware, or both without departing from the scope of the present disclosure.
• software components may be implemented as hardware components and vice-versa.
• Software in accordance with the present disclosure, such as program code and/or data, may be stored on one or more computer readable mediums. It is also contemplated that software identified herein may be implemented using one or more general purpose or specific purpose computers and/or computer systems, networked and/or otherwise. Where applicable, the ordering of various steps described herein may be changed, combined into composite steps, and/or separated into sub-steps to provide features described herein.

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• Physics & Mathematics (AREA)
• Acoustics & Sound (AREA)
• Signal Processing (AREA)
• Multimedia (AREA)
• General Physics & Mathematics (AREA)
• Amplifiers (AREA)
• Circuit For Audible Band Transducer (AREA)

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