Patent Publication Number: US-2006013408-A1

Title: Audio device with active noise cancellation

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
      This application claims the priority benefit of Taiwan application serial no. 93120944, filed Jul. 14, 2004.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an audio device. More particularly, the present invention relates to an audio device equipped with an active noise cancellation function.  
      2. Description of the Related Art  
      Portable audio device has been in our everyday life for a long time. The popularity had experienced a boom in mid 70&#39;s when Sony began marketing their famous “Walkman” line of product, it&#39;s so popular that the product name “Walkman” even became a synonym of portable audio device. During that period of time, such device relied on magnetic cassette tape as major storage media.  
      In the early 1990s, the audio industry has been affected by the digital revolution so that various type of digital audio formats start to infiltrate the mechanical/analog media market. As the prices of digital processing chips fall and the fabrication process and hardware architecture continue to improve, more and more portable audio equipment uses digital hardware. With time, digital portable audio devices such as MP3, WMA players have become the mainstream products in the market. However, it does not matter if the portable audio device operates in an analog or digital format, the environment may sometimes render the device unusable. For example, in a noisy public place, the user can hardly enjoy a musical playback by listening through a headset. In brief, noise in the environment is one big problem for the listener of a portable audio device.  
       FIG. 1  is a block diagram showing a conventional digital audio device having an active noise cancellation headset. To combat noise problem, an active noise cancellation headset (ANC) headset has been developed. As shown in  FIG. 1 , the ANC headset  120  has an active noise cancellation (ANC) control circuit  110 . The ANC headset  120  is also coupled to an audio device  130 . The audio device  130  comprises an audio processor  132  for processing audio data and providing audio playback signals to the speaker  122  inside the headset  120  and a power supply unit  134  for providing the power necessary for driving the audio processor  132 .  
      The ANC headset  120  further comprises a receiver  124  for sensing any noise inside the ANC headset  120  and submitting the noise signal to the ANC control circuit  110 . The ANC control circuit comprises analog ANC control module  112 , a power amplifier  116  and a feedback processor  118 . The analog ANC control module  112  actively cancels the noise inside the ANC headset  120  according to the output from the ANC headset  120 . The ANC control circuit  110  also includes a power supply unit  114  for providing the power necessary for driving the analog ANC control module  112 .  
      Although the conventional ANC control headset  120  is able to reduce noise interference in most audio playback equipment such as MP3, the ANC headset  120  is rather bulky. Furthermore, the provision of a power supply unit  114  inside the ANC headset  120  for driving the control circuit also adds some weight to the ANC headset  120 . One other major defect of current ANC headset based on analog circuit is that, the frequency response of the headset can be heavily affected by the onset of ANC circuit. The playback quality differs drastically upon switching on/off of ANC function. This interaction between ANC circuit and headset frequency response has been one of the major problem in introducing ANC function into audio devices.  
     SUMMARY OF THE INVENTION  
      Accordingly, at least one objective of the present invention is to provide an audio device with active noise cancellation function integrated so that when coupling with a simple headset/microphone combination, the effect of noise on the music listening can be minimized.  
      At least a second objective of the present invention is to provide an audio device integrated with active noise cancellation that can reduce the volume and weight of an ANC headset by sharing power supply and certain circuit.  
      At least a third objective of the present invention is to provide an digital audio device integrated with active noise cancellation function, so that the interaction of the audio playback and ANC function can be tuned together so that the variation of headset frequency response can be minimized upon switching ANC function.  
      To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides an audio device with active noise cancellation for driving a stereo headset. The audio device comprises an audio processor and an analog active noise cancellation (ANC) control module. The audio processor processes audio data and drives the stereo headset. The analog ANC control module actively cancels any noise generated inside the stereo headset according to a feedback signal. The audio device further comprises a power amplifier and a feedback processor. The power amplifier is coupled to the output of the audio processor and the analog ANC control module. The power amplifier amplifies the output from the audio processor and the analog ANC control module and submits the amplified signals to the stereo headset. The feedback processor receives noise signals detected from the stereo headset and provides a feedback audio signal to the analog ANC control module.  
      In the embodiment of the present invention, the audio device further comprises a power supply unit for providing electrical power to the audio processor and the ANC control module.  
      Preferably, the stereo headset further comprises an audio source and a detecting source. The audio source is coupled to the power amplifier for audio playback. The detecting source is used for sensing the noise inside the stereo headset and outputting the detected noise signal to the feedback processor. In the embodiment of the present invention, the audio source is a speaker and the detecting source is an microphone.  
      The present invention also provides an audio device with active noise cancellation that can be coupled to a stereo headset for driving the headset. The audio device comprises a digital audio processor for processing audio data and driving the stereo headset to produce source. Furthermore, the digital audio processor also has a active noise cancellation (ANC) function. Hence, the audio processor can actively cancel the inference from noise inside the stereo headset. In addition, the audio device further comprises a power amplifier and a feedback processor. The power amplifier is coupled to the output of the audio processor for amplifying the output from the audio processor and submitting the amplified signal to the stereo headset. The feedback processor receives the noise signal detected by stereo headset and generates a feedback audio signal to the audio processor.  
      In the embodiment of the present invention, the digital ANC function is implemented in digital processing format.  
      In an alternative embodiment, the present invention further comprises an analog ANC control module having an output coupled to the power amplifier. The analog ANC control module receives the feedback audio signal and actively cancels the interference from the noise having a second frequency bandwidth inside the stereo headset.  
      In addition, the power supply unit also provides electrical power to the ANC control module.  
      In brief, the ANC control module of the present invention minimizes the effect of noise on the user of a stereo headset. The present invention also permits the incorporation of a digital ANC unit inside the audio processor so that the noise within a narrow bandwidth can also be eliminated. Furthermore, the analog ANC control module is not set up within the stereo headset so that the volume of the stereo headset can be reduced. In addition, both the analog ANC control module and the audio processor use the same power supply unit. Hence, overall weight of the audio device can be reduced.  
      It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.  
       FIG. 1  is a block diagram showing a conventional digital audio device having an active noise cancellation headset.  
       FIG. 2  is a block diagram showing an audio device having active noise cancellation function according to a first embodiment of the present invention.  
       FIG. 3  is a block diagram showing an audio device having active noise cancellation function according to a second embodiment of the present invention.  
       FIG. 4  is a block diagram showing an audio device having active noise cancellation function according to a third embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.  
       FIG. 2  is a block diagram showing an audio device having active noise cancellation function according to a first embodiment of the present invention. As shown in  FIG. 2 , the present invention provides an audio device  210  suitable for driving a stereo headset  230 . The present invention may apply to a thumb disk with music playing function. Moreover, the stereo headset  230  is a unit having a unidirectional playback earplug and a feedback receiver but no conventional ANC circuit inside. Inside the audio device  210 , the output from an audio processor  212  and an analog audio noise cancellation (ANC) control module  214  are transmitted to the stereo headset  230  through a power amplifier  216 . Meanwhile, the stereo headset  230  also transmits signals corresponding to the noise detected inside the headset  230  to a feedback processor  218  inside the audio device  210 .  
      As shown in  FIG. 2 , the audio processor  212  processes audio data such as MP3 music files. The output from the audio processor  212  and the analog ANC control module  214  are both sent to the power amplifier  216 . The power amplifier  216  amplifies the output from the audio processor  212  and the analog ANC control module  214  before sending the amplified output to the stereo headset  230  for playing the audio data processed by audio processor  230  on the stereo headset  230 .  
      In general, the stereo headset  230  comprises an audio source  232  and a detecting source  234 . The audio source  232  receives the output from the power amplifier  216 . The detecting source  234  senses the noise inside the stereo headset  230  and transmits a noise-related signal to the feedback processor  218 . In the present embodiment, the audio source  232  can be a speaker and the detecting source  234  can be an microphone, for example.  
      After the power amplifier  216  has amplified the output from the audio processor  212 , the amplified signal is transmitted to the stereo headset  230  for a playback to listener. In the meantime, the detecting source  234  senses the noise inside the stereo headset  230  and transmits a corresponding signal to the feedback processor  218 . The noise within the stereo headset  230  can be any sound produced by the surrounding. After picking up an output signal from the detecting source  234 , the feedback processor  218  amplifies the output signal to generate and provide a feedback audio signal to the analog ANC control module  214 .  
      On receiving the feedback audio signal from the feedback processor  218 , the analog ANC control module  214  will produce a noise cancellation signal to the power amplifier  216  through a few simple internal transfer circuits. Thus, the power amplifier  216  can amplify both the noise cancellation signal and the output of the audio processor  212  before sending them to the stereo headset  230 . Ideally, the noise cancellation signal is out of phase with the audio noise signal. In other words, the noise cancellation signal is able to suppress the noise inside the stereo headset  230 . In practice, due to imperfection in the circuit devices, the noise cancellation signal can hardly be exactly out of phase with the audio noise signal. Yet, no matter what, the stereo headset  230  will at least output a portion noise cancellation signal to minimize the noise interference and improve the quality of playback sound.  
      Furthermore, the present invention may comprise a power supply unit  222  such as a battery module coupled to the audio processor  212  and the analog ANC control module  214  for providing necessary power for driving the two units.  
      In the present embodiment, the audio device  210  has incorporated the ANC function so that the stereo headset on the user&#39;s head can be simplified to include a typical playback portion and a simple feedback detecting source  234  such as an microphone only. In other words, the design is able not only to reduce the weight of the headset but also to cancel environmental noise.  
       FIG. 3  is a block diagram showing an audio device having active noise cancellation function according to a second embodiment of the present invention. As shown in  FIG. 3 , an audio device  310  is provided to eliminate interfering noise from a narrow frequency band. The audio processor  312  inside the audio device  310  has a digital ANC control module  314 . The digital ANC control module  314  provides the audio processor  312  with a digital ANC function for eliminating noise interference from a narrow frequency band.  
      Similarly, the audio device  310  of the present embodiment matches with the operation of a stereo headset  330 . Inside the audio device  310 , the output of the audio processor  312  is coupled to the power amplifier  316 . After amplifying the output from the audio processor  312 , the power amplifier  316  transmits the amplified output signal to the stereo headset  330 . In addition, the audio device  310  further comprises a feedback processor  318  for receiving noise signal from the stereo headset  330  and transmitting a feedback audio signal to the audio processor  312 .  
      Because the audio processor  312  encloses the digital ANC control module  314 , the digital ANC control module  314  will provide the output from the audio processor  312  with a noise cancellation signal as shown in the first embodiment. Therefore, when the stereo headset  330  is playing back audio message, the noise cancellation signal will cancel some of the interference noise resulting from a narrow frequency band. In the present embodiment, the digital ANC control module  314  can effect a noise cancellation by performing a digital signal processing operation.  
      Furthermore, the audio device  310  may comprises a power supply unit  322  coupled to the audio processor  312  for providing electrical power to drive the audio processor  312 .  
      In the present embodiment, the stereo headset  330  comprises an audio source  332  and a detecting source  334 . The audio source  332  receives an output of the power amplifier  316 . The output of the detecting source  334  is similarly coupled to the feedback processor  318 . Since the audio source  332  and the detecting source  334  inside the stereo headset  330  operate in a manner similar to the stereo headset  230  in the first embodiment, detailed description is omitted.  
      The present embodiment is very similar to the first embodiment in that the audio device  310  has incorporated the ANC function. Hence, the stereo headset on the user&#39;s head can be simplified to include a typical playback portion and a simple feedback detection unit  334  such as a microphone only. All in all, the design is able not only to reduce the weight of the headset but also to cancel environmental noise.  
       FIG. 4  is a block diagram showing an audio device having active noise cancellation function according to a third embodiment of the present invention. As shown in  FIG. 4 , the audio device  410  in the present embodiment is a hybrid between the audio device  210  of the first embodiment and the audio device  310  of the second embodiment of the present invention. This arrangement is particularly suitable for removing wide as well as narrow band interfering noise content simultaneously. The audio device comprises an audio processor  412  and an analog ANC control module  416 . The output from the audio processor  412  and the analog ANC control module  416  are coupled to the power amplifier  418 . The output of feedback processor  416  is coupled to the audio processor  412  and the analog ANC control module  416 . The audio processor  412  also encloses a digital ANC control module  414  so that the audio processor  412  has the capacity to perform typical digital ANC function. The audio device  410  further comprises a power supply unit  424  for providing electrical power to drive the audio processor  412  and the analog ANC control module  416 .  
      The third embodiment is actually a combination of the operating principle and performance level of the first and the second embodiment. Aside from canceling the multi-band noise described in the first embodiment, the audio device  410  of the present embodiment also eliminates the narrow band noise described in the second embodiment as well. Hence, the third embodiment of the present invention is able to provide a better audio noise cancellation than the previous two embodiments.  
      In summary, major advantages of the present invention at least includes:  
      1. The ANC circuit is installed inside the audio device instead of the stereo headset. Hence, overall volume of the ANC stereo headset is reduced.  
      2. The analog ANC control module uses simple logic circuit connection so that simple circuits can be deployed to increase yield and system reliability and lower production cost.  
      3. The phase difference of the audio signal due to a time delay in the noise feedback mechanism of the ANC stereo headset can be used to cancel in-head effect as well.  
      4. An ANC control module can be disposed inside the audio processor for an effective cancellation of noise interference from a narrow frequency band.  
      5. Both the audio processor and the analog ANC control module are driven by a single power supply unit so that weight can be reduced.  
      6. The audio device may integrate an audio processor having a digital ANC control module therein and an analog control module together so that interference from both broad band and narrow band noise can be attenuated.  
      It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.