Abstract:
Mobile devices such as mobile phones have always-on modes using sensors which respond to changes in the environment. A mobile device is described comprising a loudspeaker; a controller having an input coupled to the loudspeaker. The controller is operable in a first mode of operation to detect an electrical signal generated by the loudspeaker in response to an acoustic input signal. This signal can be used to activate further circuitry. Using a loudspeaker as an acoustic sensor may reduce the power consumption of the mobile device.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority under 35 U.S.C. §119 of European patent application no. 14184894.5, filed Sep. 16, 2015 the contents of which are incorporated by reference herein. 
     This invention relates to a mobile device having a first mode of operation and a further mode of operation. 
     Mobile devices such as mobile phones, ultrabooks, tablet PCs typically have “always-on” functions which continuously sense the environment. When an appropriate environmental change is detected, the always on function is triggered to perform actions such as device wake-up, and voice keyword detection. These “always-on” functions have very low power requirements, typically lower than 1 milliwatts. These functions are typically implemented using sensors and low power hardware components such as integrated circuits which function independently from the high power main or system processor. 
     In case of voice activation in a mobile phone the main processor may be only woken up if a dedicated keyword is recognized. A multi-stage activation is usually applied. The mobile device  100  shown in  FIG. 1  has an audio level monitoring circuit  10  connected to a digital signal processor (DSP)  18  which implements a voice activity detector  12  and keyword detector  14  as algorithms running on the DSP  18 . 
     The microphone  16  is typically an analog or digital MEMS microphone or an electret condenser microphone connected to a power supply  20 . In a first stage if an acoustic input sensed by the microphone includes non-stationary sound components, this may indicate a potential voice command to activate the mobile phone. In this case the audio level monitoring circuit  10  generates an activation signal which typically may be an interrupt request. This interrupt request activates the second stage by enabling the voice activity detector  12 . If the acoustic input is determined to be speech by the voice activity detector  12 , then a third stage is activated whereby the voice activity detector  12  enables or activates the keyword detector  14 . As voice activity detector  12  and keyword detector  14  are implemented on a DSP then the activation signal for the third stage can be a software interrupt. If a keyword is detected by keyword detector  14  the digital signal processor  18  may generate a hardware interrupt request to a main processor (not shown). The interrupt request from the digital signal processor  18  may then wake up the main processor. A multistage power activation minimizes power consumption, however because of the always-on requirement, the first stage always consumes some power. 
     Various aspects of the invention are defined in the accompanying claims. In a first aspect there is defined a method of operation of a mobile device having a first mode of operation and a further mode of operation, the mobile device comprising a loudspeaker, the method comprising in the first mode of operation detecting an electrical signal generated by the loudspeaker in response to an acoustic stimulus, generating an activation signal in response to the detected acoustic input, and enabling the further mode of operation in response to the activation signal. 
     The loudspeaker of the mobile device may generate a detectable electrical response to an acoustic stimulus such as speech or clapping or some other audio impulse. Since the loudspeaker does not require a power supply, the power consumption of the first always-on stage of a multi-stage activation sequence may be reduced. 
     In embodiments enabling the further mode of operation may comprise activating a system processor in response to the activation signal. 
     In embodiments, enabling the further mode of operation may comprise activating a digital processor in response to the activation signal. 
     In embodiments, enabling the further mode of operation may comprise enabling a microphone in response to the activation signal. 
     In embodiments, enabling the further mode of operation may comprise detecting an electrical signal generated by the microphone in response to a further acoustic stimulus. 
     By using the loudspeaker to detect an initial acoustic input before activating the microphone, the power consumption of an always on sensing mode may be considerably reduced. This is because the microphone in a mobile device such as a mobile phone typically consumes 10 μA to 500 μA depending on the microphone type. In embodiments the first mode of operation may have a lower power consumption than the further mode of operation whereas the loudspeaker may consume no power unless driven by an amplifier. 
     In embodiments, the first mode of operation is a standby mode and wherein the power consumption of the standby mode is less than 1 mW. 
     Embodiments may be include a method of voice activation of mobile devices. 
     In a second aspect there is described a mobile device having a first mode of operation and a further mode of operation, the mobile device comprising: a loudspeaker; a controller having an input coupled to the loudspeaker; wherein the controller is operable in a first mode of operation to detect an electrical signal generated by the loudspeaker in response to an acoustic input signal, and to generate an activation signal in response to the detected acoustic input; and wherein the mobile device is operable to enable a further mode of operation in response to the activation signal. 
     In embodiments, the mobile device comprises an audio amplifier switchably coupled to the loudspeaker and wherein the controller is switchably coupled to the loudspeaker, wherein the controller is coupled to the loudspeaker in the first mode of operation and the audio amplifier is coupled to the loud speaker in the further mode of operation. 
     In embodiments the controller further comprises a first level detector having a first response time and a second level detector having a second different response time; wherein of the inputs of the first level detector and the second level detector are coupled to the loudspeaker in the first mode of operation, and the respective outputs of the first level detector and the second level detector are coupled to respective inputs of a comparator and the comparator output is coupled to the output of the detector and wherein the controller is operable to generate an activation signal in response to a non-stationary sound source. 
     In embodiments, the mobile device may comprise a microphone switchably coupled to a power supply and wherein the controller is configured to enable the microphone in response to the activation signal. 
     In embodiments, the mobile device may comprise a codec coupled to the microphone and the controller and wherein the controller is operable to enable the codec in response to the activation signal and wherein the codec is operable to generate a further activation signal in response to the activation signal. 
     The codec may be an audio codec implemented on a digital signal processor. 
     In embodiments, the mobile device may further comprise a system processor and wherein the controller is operable to enable the system processor in response to the further activation signal. 
     A mobile device may be one of a mobile phone, a laptop computer, a tablet computer and an mp3 player. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the figures and description like reference numerals refer to like features Embodiments of the invention are now described in detail, by way of example only, illustrated by the accompanying drawings in which: 
         FIG. 1  Shows a known method of operation of a mobile device. 
         FIG. 2  Illustrates a mobile device according to an embodiment. 
         FIG. 3  Shows a mobile device according to an embodiment. 
         FIG. 4A  illustrated a mobile device according to an embodiment.  FIG. 4B  shows an example level detector. 
         FIG. 5  illustrates an electrical signal generated by a microphone and a loudspeaker in response to an acoustic stimulus. 
         FIG. 6  Illustrates an example method of operation according to an embodiment. 
         FIG. 7  shows a further example method of operation according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 2  illustrates a mobile device  200 . Audio amplifier  32  may have an audio input  30  and an audio output  34  which may be a differential output. Audio amplifier  32  may be a class D amplifier. The audio output  34  may be connected to a loudspeaker  38  via a signal router  40  which is controlled by a control input  36 . A controller  46 , may have an input  42  which may be a differential input. Controller input  42  may be connected to a loudspeaker  38  via the signal router  40  which may route a signal between the loudspeaker  38  and the audio output  34  or the controller input  42 . The signal router may for example be a multiplexer, de-multiplexer or switch. The controller  46  may have a controller activation output  44 . The controller  46  may be connected to the control input  36  of the signal router  40 . 
     In operation, the mobile device  200  may be in a first mode of operation in which the controller inputs  42  are connected to the loudspeaker  38  by the signal router  40 . The speaker amplifier  32  may be disconnected from the loudspeaker  38  by the signal router  40 . 
     In the first mode of operation, the controller  46  may be powered up. In the first mode of operation of the mobile device  200 , other circuitry such as the amplifier  32  and a system processor (not shown) may be powered down. In examples of mobile devices, the loudspeaker  38  may be for example a receiver speaker in a mobile phone or a hands-free speaker in a mobile phone. The loudspeaker  38  may generate an electrical signal in response to an acoustic stimulus. The acoustic stimulus may be for example speech or clapping or some other audio stimulus. The electrical signal generated by the loudspeaker  38  may be detected by the controller  46 . The controller  46  may generate an activation signal on the controller activation output  44  in response to the electrical signal received on the controller input  42 . The controller  46  may include for example a comparator in which a comparison is made between the detected electrical signal and a predetermined threshold value. 
     The activation signal generated may enable or activate one or more further circuits such as a digital signal processor (not shown) of the mobile device  200 . Following the activation of further circuits, the mobile device  200  may be configured in a second mode of operation. In the second mode of operation, the amplifier  32  may be connected to the loudspeaker via the signal router  40 . In the normal operating mode, the controller inputs  42  may be disconnected from the loudspeaker  38 . The controller  46  may disconnect the controller inputs  42  from the loudspeaker  38  once an activation signal is generated on the controller activation output  44 . 
     In the first operating mode, the loudspeaker  38  may not require a power supply. In contrast, to function correctly, a microphone in a mobile device may need to be enabled and may consume current rating typically from 10 μA to 500 μA depending on the microphone type. Consequently an always-on function can be implemented which consumes much less power, for example less than 1 μA. For a mobile device such as a mobile phone, a first mode of operation may be a standby mode. A second mode of operation may be a normal operating mode whereby, for example phone calls can be made or received. Alternatively in a smart phone, a mode of operation may be any mode in which the display screen is active. For a mobile device such as a mobile audience music player, a first mode of operation may be a standby mode. A normal operating mode may be a mode in which audio may be output through the loudspeaker  38 . 
     In some examples of the mobile device, the audio amplifier may be powered down in a first mode of operation and only powered up in a second mode of operation. In this case, the signal router  40  may be omitted. The skilled person will appreciate that the signal router  40  may be implemented for example as a multiplexor using transistors such as MOS transistors. The controller  46  may be implemented in hardware, or a combination of hardware and software. The hardware may include analog and digital circuits. 
       FIG. 3  illustrates a mobile device  300 . The mobile device  300  may have a microphone  16 , and loudspeaker  38 . Audio amplifier  32  may have an audio input  30  and an audio output  34  which may be a differential input. Audio amplifier  32  may be a class D amplifier. The audio output  34  may be connected to a loudspeaker  38  via a signal router  40  which is controlled by a control input  36 . A controller  46 , may have an input  42  which may be a differential input. Controller input  42  may be connected to a loudspeaker  38  via the signal router  40 . A controller  46  may be connected to the signal router control input  36 . The controller  46  may have a controller activation output  44 . Microphone  16  may be connected to a power supply  52  via a microphone enable switch  48 . The controller activation output  44  may be connected to a control input of the microphone enable switch  48 . The skilled person will appreciate that for example the microphone enable switch  48  may be a MOS transistor having a gate connected to the controller activation output  44 , one of the source and drain connected to the power supply  52 , and the other of the source and drain connected to the supply input of the microphone  48 . The microphone enable switch  48  may be integrated together with a microphone and connected to a microphone enable input. 
     In operation, the mobile device  300  may be in a first mode of operation in which the controller inputs  42  are connected to the loudspeaker  38  by the signal router  40 . The speaker amplifier  32  may be disconnected from the loudspeaker  38  by the signal router  40 . In the first mode of operation, the controller  46  may be powered up. In the first mode of operation of the mobile device  300 , other circuitry such as the amplifier  32  and a system processor (not shown) may be powered down. The loudspeaker  38  may be for example a receiver speaker in a mobile phone or a hands-free speaker in a mobile phone. The loudspeaker  38  may generate an electrical signal in response to an acoustic stimulus. The acoustic stimulus may be for example speech or clapping or some other audio stimulus. This electrical signal may be detected by the controller  46 . The controller  46  may generate an activation signal on the controller activation output  44  in response to the electrical signal received on the controller input  42 . The activation signal on the controller activation output  44  may enable the microphone  16  by connecting it to the power supply  20  via the microphone enable switch  48 . Once enabled, the microphone  16  may be used to detect further acoustic stimuli. Since the loudspeaker  38  may consume much less current than the microphone  48 , a multistage activation may be implemented using progressively larger current consuming components. During the activation of the mobile device from a first mode of operation to a second mode of operation, the loudspeaker  38  may be used in a first activation stage and the microphone  16  may be used in a second activation stage. Alternatively, the loudspeaker  38  may be used in all activation stages. 
       FIG. 4 a    shows a mobile device  400 . Audio amplifier  32  may have an audio input  30  and an audio output  34  which may be a differential output. Audio amplifier  32  may be a class D amplifier. The audio output  34  may be connected to a loudspeaker  38  via a signal router  40  which is controlled by a control input  36 . A controller  48  which may be responsive to a non-stationary sound may have an input  42  which may be a differential input. The controller  48  may have a controller activation output  44 . Controller input  42  may be connected to a loudspeaker  38  via the signal router  40  which may be controlled by a control input  36 . The controller input  42  may be connected to a first level detector  64 . The first level detector  64  may have a first time constant. The controller input  42  may be connected to a second level detector  66 . The second level detector  66  may have a second different time constant. The time constant of the respective level detectors  64 , 66  may determine the response time of the level detector to an acoustic input. The first level detector may have a shorter time constant than the second level detector. An output of the first level detector may be connected to a first input of a comparator  62 . An output of the second level detector  66  may be connected to a second input of the comparator  62 . An output of the comparator may be connected to control logic  68 . The control logic  68  may be connected to the controller activation output  44 . The control logic  68  may be connected to the signal router control input  36 . The controller activation output  44  may be connected to an input of a an audio codec  54 . Audio codec  54  may be implemented by a programmable digital signal processor or a dedicated circuit. The control logic  68  may have a control input  70  connected to an output of the main processor  60 . The control input  70  may control a reset function of the control logic  68  for example. Alternatively the control input  70  may also control programmable registers in the control logic  68 . 
     System processor  60  which may be a microprocessor may have an output connected to the control input  36  of the signal router  40 . System processor  60  may have an audio output connected to the input  30  of the amplifier  32 . audio codec  54  may have an input connected to the microphone  16  and an output  58  connected to a control input of the microphone enable switch  48 . 
     The first level detector  64  and the second level detector  66  may typically be implemented as a rectifier  72 , 72 ′ connected to an integrator  74 , 74 ′ as shown in  FIG. 4B . The time constant of the integrator  74  may typically determine the response time of the first and second level detectors  64 ,  66 . In operation, the mobile device  400  may be in a first mode of operation in which the controller inputs  42  are connected to the loudspeaker  38  by the signal router  40 . The speaker amplifier  32  may be disconnected from the loudspeaker  38  by the signal router  40 . In the first mode of operation, the controller  48  may be powered up. Controller  48  may always have power applied. In the first mode of operation of the mobile device  400 , other circuitry such as the amplifier  32  and the system processor  60  may be powered down. The loudspeaker  38  may be for example a receiver speaker in a mobile phone or a hands-free speaker in a mobile phone. The loudspeaker  38  may generate an electrical signal in response to an acoustic stimulus. The acoustic stimulus may be for example speech or clapping or some other audio stimulus. This electrical signal may be detected by the controller  48 . In operation of the controller  48 , in the case of stationary noise input, the output of the first level detector  64  and the second level detector  66  may be comparable or approximately equal. In the case of non-stationary noise, the first level detector may react quicker than the second level detector and its output will be higher than that of the second level detector. Therefore, when the ratio between the first level detector output and the second level detector output is greater than a certain value, the audio input may be considered as being non-stationary. The comparator  62  output may change when a non-stationary signal is detected. The control logic  68  may generate an activation signal when the comparator output changes indicating that a non-stationary acoustic input has been detected. The control logic  68  may switch the signal router  36  to connect the loudspeaker  38  to the amplifier  32 . 
     The activation signal on the controller activation output  44  may enable or activate the audio codec  54 . The audio codec  54  may activate or enable the microphone  48 . The microphone  16  may generate electrical signals in response to a further acoustic stimulus. The audio codec  54  may process the input signal received from the microphone  16  to determine whether the subsequent acoustic input signal is speech. Audio codec  54  may activate the system processor  60  for example by generating an interrupt on interrupt output  56 . Once the system processor  60  is activated, the controller  48  may connect the loudspeaker  38  to the outputs of the audio amplifier  32  by controlling the signal router  40 . The mobile device  400  may then be in a second mode of operation. 
     The first mode of operation may be a low power or standby mode. The second mode of operation may be a higher power mode of operation than the first mode 
       FIG. 5  shows a graph  500  of the response of a loudspeaker  10  audio signal shown on the graph line  80 . Graph  500  shows the response of a microphone to the same audio signal audio signal shown on the graph line  82 . The x-axis is the sample number, and the y-axis shows the output in decibels. As can be clearly seen, the response of the loudspeaker  80  is noisier than the response of the microphone  82 . However the non-stationary components  84  of the acoustic input generate a larger signal input on the input of the loudspeaker than the stationary components and so can be discriminated from the background noise. 
       FIG. 6  shows an example method of operation of the mobile device  600 . In step  90  a mobile device may be in a low power always on mode. In this mode, many components of the mobile device will be disabled, such as the microphone and a system processor. In step  92  non-stationary sound components which may be speech may be detected using the loudspeaker. In step  94  an interrupt request may be generated from the response of the loudspeaker to an acoustic input having non-stationary sound components. This may be the first stage of a multistage activation process. 
       FIG. 7  shows a method of voice activation of a mobile device  700 . In step  110 , a mobile device may be in a low power always on mode. In the always on mode a microphone may be disabled and an audio amplifier may be disabled. In step  112  non-stationary sound components in an acoustic input may be detected by the response of the loudspeaker to the acoustic input. If non-stationary sound components are detected then in step  114  an activation signal, which may be an interrupt request, may be generated indicating that a possible speech signal has been detected. The interrupt generated in  114  may enable a microphone and codec in step  116 . As more and more components are enabled then the power consumption of the mobile device may increase. In step  118  the method determines whether or not speech has been detected by the microphone. If no speech has been detected then the method may return to step  110  in which the microphone is disabled and the codec, which may be implemented in a digital signal processor, may also be disabled. Returning to step  118 , if speech has been detected then a keyword detector may be enabled in step  120 . In step  122  the keyword detector may determine whether a keyword has been detected. If a keyword is detected a further interrupt request may be generated in step  124 . The further interrupt request may wake up a system processor and may enable an audio amplifier in step  126 . Following the activation of the main system processor, the mobile device may be in a second mode of operation in step  128 . 
     Although the appended claims are directed to particular combinations of features, it should be understood that the scope of the disclosure of the present invention also includes any novel feature or any novel combination of features disclosed herein either explicitly or implicitly or any generalisation thereof, whether or not it relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as does the present invention. 
     Features which are described in the context of separate embodiments may also be provided in combination in a single embodiment. Conversely, various features which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub combination. 
     The applicant hereby gives notice that new claims may be formulated to such features and/or combinations of such features during the prosecution of the present application or of any further application derived therefrom. 
     For the sake of completeness it is also stated that the term “comprising” does not exclude other elements or steps, the term “a” or “an” does not exclude a plurality, a single processor or other unit may fulfil the functions of several means recited in the claims and reference signs in the claims shall not be construed as limiting the scope of the claims.