Patent Publication Number: US-10332544-B2

Title: Microphone and corresponding digital interface

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 14/533,652, filed Nov. 5, 2014, which is a continuation-in-part of U.S. patent application Ser. No. 14/282,101, filed May 20, 2014, now U.S. Pat. No. 9,745,923, which claims the benefit of and priority to U.S. Provisional Application No. 61/826,587, filed May 23, 2013, and U.S. Provisional Application No. 61/901,832, filed Nov. 8, 2013, the entire contents of each of which are incorporated by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     This application relates to acoustic activity detection (AAD) approaches and voice activity detection (VAD) approaches, and their interfacing with other types of electronic devices. 
     BACKGROUND 
     Voice activity detection (VAD) approaches are important components of speech recognition software and hardware. For example, recognition software constantly scans the audio signal of a microphone searching for voice activity, usually, with a MIPS intensive algorithm. Since the algorithm is constantly running, the power used in this voice detection approach is significant. 
     Microphones are also disposed in mobile device products such as cellular phones. These customer devices have a standardized interface. If the microphone is not compatible with this interface it cannot be used with the mobile device product. 
     Many mobile devices have speech recognition included with the mobile device. However, the power usage of the algorithms are taxing enough to the battery that the feature is often enabled only after the user presses a button or wakes up the device. In order to enable this feature at all times, the power consumption of the overall solution must be small enough to have minimal impact on the total battery life of the device. As mentioned, this has not occurred with existing devices. 
     Because of the above-mentioned problems, some user dissatisfaction with previous approaches has occurred. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the disclosure, reference should be made to the following detailed description and accompanying drawings wherein: 
         FIG. 1A  is a block diagram of an acoustic system with acoustic activity detection (AAD); 
         FIG. 1B  is a block diagram of another acoustic system with acoustic activity detection (AAD); 
         FIG. 2  is a timing diagram showing one aspect of the operation of the system of  FIG. 1 ; 
         FIG. 3  is a timing diagram showing another aspect of the operation of the system of  FIG. 1 ; 
         FIG. 4  is a state transition diagram showing states of operation of the system of  FIG. 1 ; 
         FIG. 5  is a table showing the conditions for transitions between the states shown in the state diagram of  FIG. 4 . 
     
    
    
     Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity. It will be appreciated further that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. It will also be understood that the terms and expressions used herein have the ordinary meaning as is accorded to such terms and expressions with respect to their corresponding respective areas of inquiry and study except where specific meanings have otherwise been set forth herein. 
     DETAILED DESCRIPTION 
     Approaches are described herein that integrate voice activity detection (VAD) or acoustic activity detection (AAD) approaches into microphones. At least some of the microphone components (e.g., VAD or AAD modules) are disposed at or on an application specific circuit (ASIC) or other integrated device. The integration of components such as the VAD or AAD modules significantly reduces the power requirements of the system thereby increasing user satisfaction with the system. An interface is also provided between the microphone and circuitry in an electronic device (e.g., cellular phone or personal computer) in which the microphone is disposed. The interface is standardized so that its configuration allows placement of the microphone in most if not all electronic devices (e.g., cellular phones). The microphone operates in multiple modes of operation including a lower power mode that still detects acoustic events such as voice signals. 
     In many of these embodiments, at a microphone analog signals are received from a sound transducer. The analog signals are converted into digitized data. A determination is made as to whether voice activity exists within the digitized signal. Upon the detection of voice activity, an indication of voice activity is sent to a processing device. The indication is sent across a standard interface, and the standard interface is configured to be compatible to be coupled with a plurality of devices from potentially different manufacturers. 
     In other aspects, the microphone is operated in multiple operating modes, such that the microphone selectively operates in and moves between a first microphone sensing mode and a second microphone sensing mode based upon one or more of whether an external clock is being received from a processing device, or whether power is being supplied to the microphone. Within the first microphone sensing mode, the microphone utilizes an internal clock, receives first analog signals from a sound transducer, converts the first analog signals into first digitized data, determines whether voice activity exists within the first digitized signal, and upon the detection of voice activity, sends an indication of voice activity to the processing device an subsequently switches from using the internal clock to receiving an external clock. Within the second microphone sensing mode, the microphone receives second analog signals from a sound transducer, converts the second analog signals into second digitized data, determines whether voice activity exists within the second digitized signal, and upon the detection of voice activity, sends an indication of voice activity to the processing device, and uses the external clock supplied by the processing device. 
     In some examples, the indication comprises a signal indicating voice activity has been detected or a digitized signal. In other examples, the transducer comprises one of a microelectromechanical system (MEMS) device, a piezoelectric device, or a speaker. 
     In some aspects, the receiving, converting, determining, and sending are performed at an integrated circuit. In other aspects, the integrated circuit is disposed at one of a cellular phone, a smart phone, a personal computer, a wearable electronic device, or a tablet. In some examples, the receiving, converting, determining, and sending are performed when operating in a single mode of operation. 
     In some examples, the single mode is a power saving mode. In other examples, the digitized data comprises PDM data or PCM data. In some other examples, the indication comprises a clock signal. In yet other examples, the indication comprises one or more DC voltage levels. 
     In some examples, subsequent to sending the indication, a clock signal is received at the microphone. In some aspects, the clock signal is utilized to synchronize data movement between the microphone and an external processor. In other examples, a first frequency of the received clock is the same as a second frequency of an internal clock disposed at the microphone. In still other examples, a first frequency of the received clock is different than a second frequency of an internal clock disposed at the microphone. 
     In some examples, prior to receiving the clock signal, the microphone is in a first mode of operation, and receiving the clock signal is effective to cause the microphone to enter a second mode of operation. In other examples, the standard interface is compatible with any combination of the PDM protocol, the I 2 S protocol, or the I 2 C protocol. 
     In other embodiments, an apparatus includes an analog-to-digital conversion circuit, the analog-to-digital conversion circuit being configured to receive analog signals from a sound transducer and convert the analog signals into digitized data. The apparatus also includes a standard interface and a processing device. The processing device is coupled to the analog-to-digital conversion circuit and the standard interface. The processing device is configured to determine whether voice activity exists within the digitized signal and upon the detection of voice activity, to send an indication of voice activity to an external processing device. The indication is sent across the standard interface, and the standard interface is configured to be compatible to be coupled with a plurality of devices from potentially different manufacturers. 
     Referring now to  FIG. 1A , a microphone apparatus  100  includes a charge pump  101 , a capacitive microelectromechanical system (MEMS) sensor  102 , a clock detector  104 , a sigma-delta modulator  106 , an acoustic activity detection (AAD) module  108 , a buffer  110 , and a control module  112 . It will be appreciated that these elements may be implemented as various combinations of hardware and programmed software and at least some of these components can be disposed on an ASIC. 
     The charge pump  101  provides a voltage to charge up and bias a diaphragm of the capacitive MEMS sensor  102 . For some applications (e.g., when using a piezoelectric device as a sensor), the charge pump may be replaced with a power supply that may be external to the microphone. A voice or other acoustic signal moves the diaphragm, the capacitance of the capacitive MEMS sensor  102  changes, and voltages are created that become an electrical signal. In one aspect, the charge pump  101  and the MEMS sensor  102  are not disposed on the ASIC (but in other aspects, they may be disposed on the ASIC). It will be appreciated that the MEMS sensor  102  may alternatively be a piezoelectric sensor, a speaker, or any other type of sensing device or arrangement. 
     The clock detector  104  controls which clock goes to the sigma-delta modulator  106  and synchronizes the digital section of the ASIC. If an external clock is present, the clock detector  104  uses that clock; if no external clock signal is present, then the clock detector  104  use an internal oscillator  103  for data timing/clocking purposes. 
     The sigma-delta modulator  106  converts the analog signal into a digital signal. The output of the sigma-delta modulator  106  is a one-bit serial stream, in one aspect. Alternatively, the sigma-delta modulator  106  may be any type of analog-to-digital converter. 
     The buffer  110  stores data and constitutes a running storage of past data. By the time acoustic activity is detected, this past additional data is stored in the buffer  110 . In other words, the buffer  110  stores a history of past audio activity. When an audio event happens (e.g., a trigger word is detected), the control module  112  instructs the buffer  110  to spool out data from the buffer  110 . In one example, the buffer  110  stores the previous approximately 180 ms of data generated prior to the activity detect. Once the activity has been detected, the microphone  100  transmits the buffered data to the host (e.g., electronic circuitry in a customer device such as a cellular phone). 
     The acoustic activity detection (AAD) module  108  detects acoustic activity. Various approaches can be used to detect such events as the occurrence of a trigger word, trigger phrase, specific noise or sound, and so forth. In one aspect, the module  108  monitors the incoming acoustic signals looking for a voice-like signature (or monitors for other appropriate characteristics or thresholds). Upon detection of acoustic activity that meets the trigger requirements, the microphone  100  transmits a pulse density modulation (PDM) stream to wake up the rest of the system chain to complete the full voice recognition process. Other types of data could also be used. 
     The control module  112  controls when the data is transmitted from the buffer. As discussed elsewhere herein, when activity has been detected by the AAD module  108 , then the data is clocked out over an interface  119  that includes a VDD pin  120 , a clock pin  122 , a select pin  124 , a data pin  126  and a ground pin  128 . The pins  120 - 128  form the interface  119  that is recognizable and compatible in operation with various types of electronic circuits, for example, those types of circuits that are used in cellular phones. In one aspect, the microphone  100  uses the interface  119  to communicate with circuitry inside a cellular phone. Since the interface  119  is standardized as between cellular phones, the microphone  100  can be placed or disposed in any phone that utilizes the standard interface. The interface  119  seamlessly connects to compatible circuitry in the cellular phone. Other interfaces are possible with other pin outs. Different pins could also be used for interrupts. 
     In operation, the microphone  100  operates in a variety of different modes and several states that cover these modes. For instance, when a clock signal (with a frequency falling within a predetermined range) is supplied to the microphone  100 , the microphone  100  is operated in a standard operating mode. If the frequency is not within that range, the microphone  100  is operated within a sensing mode. In the sensing mode, the internal oscillator  103  of the microphone  100  is being used and, upon detection of an acoustic event, data transmissions are aligned with the rising clock edge, where the clock is the internal clock. 
     Referring now to  FIG. 1B , another example of a microphone  100  is described. This example includes the same elements as those shown in  FIG. 1A  and these elements are numbered using the same labels as those shown in  FIG. 1A . 
     In addition, the microphone  100  of  FIG. 1B  includes a low pass filter  140 , a reference  142 , a decimation/compression module  144 , a decompression PDM module  146 , and a pre-amplifier  148 . 
     The function of the low pass filter  140  removes higher frequency from the charge pump. The function of the reference  142  is a voltage or other reference used by components within the system as a convenient reference value. The function of the decimation/compression module  144  is to minimize the buffer size used to compress and then store the data. The function of the decompression PDM module  146  is to pull the data apart for the control module. The function of the pre-amplifier  148  is bringing the sensor output signal to a usable voltage level. 
     The components identified by the label  100  in  FIG. 1A  and  FIG. 1B  may be disposed on a single application specific integrated circuit (ASIC) or other integrated device. However, the charge pump  101  is not disposed on the ASIC  160  in  FIGS. 1A  and is on the ASIC in the system of  FIG. 1B . These elements may or may not be disposed on the ASIC in a particular implementation. It will be appreciated that the ASIC may have other functions such as signal processing functions. 
     Referring now to  FIG. 2 ,  FIG. 3 ,  FIG. 4 , and  FIG. 5 , a microphone (e.g., the microphone  100  of  FIG. 1 ) operates in a standard performance mode and a sensing mode, and these are determined by the clock frequency. In standard performance mode, the microphone acts as a standard microphone in which it clocks out data as received. The frequency range required to cause the microphone to operate in the standard mode may be defined or specified in the datasheet for the part-in-question or otherwise supplied by the manufacturer of the microphone. 
     In sensing mode, the output of the microphone is tri-stated and an internal clock is applied to the sensing circuit. Once the AAD module triggers (e.g., sends a trigger signal indicating an acoustic event has occurred), the microphone transmits buffered PDM data on the microphone data pin (e.g., data pin  126 ) synchronized with the internal clock (e.g., a 512 kHz clock). This internal clock will be supplied to the select pin (e.g., select pin  124 ) as an output during this mode. In this mode, the data will be valid on the rising edge of the internally generated clock (output on the select pin). This operation assures compatibility with existing I 2 S compatible hardware blocks. The select pin (e.g., select pin  124 ) and the data pin (e.g., data pin  126 ) will stop outputting the clock signal and data a set time after activity is no longer detected. The frequency for this mode is defined in the datasheet for the part in question. In other examples, the interface is compatible with the PDM protocol or the I 2 C protocol. Other examples are possible. 
     The operation of the microphone described above is shown in  FIG. 2 . The select pin (e.g., select pin  124 ) is the top line, the data pin (e.g., data pin  126 ) is the second line from the top, and the clock pin (e.g., clock pin  122 ) is the bottom line on the graph. It can be seen that once acoustic activity is detected, data is transmitted on the rising edge of the internal clock. As mentioned, this operation assures compatibility with existing I 2 S compatible hardware blocks. 
     For compatibility to the DMIC-compliant interfaces in sensing mode, the clock pin (e.g., clock pin  122 ) can be driven to clock out the microphone data. The clock must meet the sensing mode requirements for frequency (e.g., 512 kHz). When an external clock signal is detected on the clock pin (e.g., clock pin  122 ), the data driven on the data pin (e.g., data pin  126 ) is synchronized with the external clock within two cycles, in one example. Other examples are possible. In this mode, the external clock is removed when activity is no longer detected for the microphone to return to lowest power mode. Activity detection in this mode may use the select pin (e.g., select pin  124 ) to determine if activity is no longer sensed. Other pins may also be used. 
     This operation is shown in  FIG. 3 . The select pin (e.g., select pin  124 ) is the top line, the data pin (e.g., data pin  126 ) is the second line from the top, and the clock pin (e.g., clock pin  122 ) is the bottom line on the graph. It can be seen that once acoustic activity is detected, the data driven on the data pin (e.g., data pin  126 ) is synchronized with the external clock within two cycles, in one example. Other examples are possible. Data is synchronized on the falling edge of the external clock. Data can be synchronized using other clock edges as well. Further, the external clock is removed when activity is no longer detected for the microphone to return to lowest power mode. 
     Referring now to  FIG. 4  and  FIG. 5 , a state transition diagram  400  ( FIG. 4 ) and transition condition table  500  ( FIG. 5 ) are described. The various transitions listed in  FIG. 4  occur under the conditions listed in the table of  FIG. 5 . For instance, transition A 1  occurs when Vdd is applied and no clock is present on the clock input pin. It will be understood that the table of  FIG. 5  gives frequency values (which are approximate) and that other frequency values are possible. The term “OTP” means one time programming. 
     The state transition diagram of  FIG. 4  includes a microphone off state  402 , a normal mode state  404 , a microphone sensing mode with external clock state  406 , a microphone sensing mode internal clock state  408  and a sensing mode with output state  410 . 
     The microphone off state  402  is where the microphone  400  is deactivated. The normal mode state  404  is the state during the normal operating mode when the external clock is being applied (where the external clock is within a predetermined range). The microphone sensing mode with external clock state  406  is when the mode is switching to the external clock as shown in  FIG. 3 . The microphone sensing mode internal clock state  408  is when no external clock is being used as shown in  FIG. 2 . The sensing mode with output state  410  is when no external clock is being used and where data is being output also as shown in  FIG. 2 . 
     As mentioned, transitions between these states are based on and triggered by events. To take one example, if the microphone is operating in normal operating state  404  (e.g., at a clock rate higher than 512 kHz) and the control module detects the clock pin is approximately 512 kHz, then control goes to the microphone sensing mode with external clock state  406 . In the external clock state  406 , when the control module then detects no clock on the clock pin, control goes to the microphone sensing mode internal clock state  408 . When in the microphone sensing mode internal clock state  408 , and an acoustic event is detected, control goes to the sensing mode with output state  410 . When in the sensing mode with output state  410 , a clock of greater than approximately 1 MHz may cause control to return to state  404 . The clock may be less than 1 MHz (e.g., the same frequency as the internal oscillator) and is used to synchronize data being output from the microphone to an external processor. No acoustic activity for an OTP programmed amount of time, on the other hand, causes control to return to state  406 . 
     It will be appreciated that the other events specified in  FIG. 5  will cause transitions between the states as shown in the state transition diagram of  FIG. 4 . 
     Preferred embodiments are described herein, including the best mode known to the inventors. It should be understood that the illustrated embodiments are exemplary only, and should not be taken as limiting the scope of the appended claims.