Abstract:
The present invention provides a signal processing circuit and a signal processing method applied to a headset. In the present invention, the signal processing circuit adjusts gain and phase of a left channel signal and a right channel signal to generate a first adjust signal, and a recorded sound from a microphone is added by the first adjust signal to cancel a coupled signal. In addition, the signal processing circuit adjusts gain and phase of the right channel signal to generate a second adjust signal, and the right channel signal is added by the second adjust signal to cancel a coupled signal; and the signal processing circuit adjusts gain and phase of the left channel signal to generate a third adjust signal, and the left channel signal is added by the third adjust signal to cancel a coupled signal.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to signal processing, and more particularly, to a signal processing circuit and a signal processing method applied to a headset. 
     2. Description of the Prior Art 
     Regarding a related art headset, when the plug of the headset is inserted into an audio jack and the headset plays audio signals with both the left and right earphones, a user&#39;s right ear may hear the sound of the left channel, and the user&#39;s left ear may hear the sound of the right channel due to the impedance of the grounding point of the audio jack, the impedance of the inner grounding point of the audio integrated circuit (IC), or the impedance of the layout trace for connecting the audio jack to the audio IC. Further, if the microphone of the headset is recording sounds at the same time, the microphone will record the sounds of the left channel and the right channel simultaneously. The above crosstalk interference degrades user&#39;s experience of using the headset. 
     SUMMARY OF THE INVENTION 
     Hence, one objective of the present invention is to provide a signal processing circuit and a signal processing method applied to a headset to reduce the aforementioned crosstalk, thereby solving the issue of the related art. 
     According to an embodiment of the present invention, a signal processing circuit applied to a headset is provided. The headset includes a left earphone, a right earphone and a microphone. The signal processing circuit receives a sound signal from the microphone, and generates audio signals to the left earphone and the right earphone, respectively. The signal processing circuit includes an analog-to-digital converter, an audio processing circuit, a first gain and phase adjuster and a first adder. The analog-to-digital converter is arranged for receiving the sound signal from the microphone, and converting the sound signal into a digital input signal. The audio processing circuit is arranged for generating a left channel signal and a right channel signal, wherein the left channel signal and the right channel signal are utilized to generate the audio signals. The first gain and phase adjuster is coupled to the audio processing circuit, and arranged to adjust gains and phases of the left channel signal and the right channel signal to generate a first adjusted signal. The first adder is coupled to the analog-to-digital converter, the first gain and phase adjuster and the audio processing circuit, and the first adder is arranged to combine the digital input signal and the first adjusted signal to generate an adjusted digital input signal to the audio processing circuit. 
     According to another embodiment of the present invention, a signal processing circuit applied to a headset is provided. The headset includes a left earphone, a right earphone and a microphone. The signal processing circuit receives a sound signal from the microphone, and generates audio signals to the left earphone and the right earphone, respectively. The signal processing circuit includes an audio processing circuit, a first gain and phase adjuster, a first adder, a first analog-to-digital converter, a second gain and phase adjuster, a second adder, and a second analog-to-digital converter. The audio processing circuit is arranged for generating a left channel signal and a right channel signal. The first gain and phase adjuster is coupled to the audio processing circuit, and arranged to adjust a gain and a phase of the right channel signal to generate a first adjusted signal. The first adder is coupled to the first gain and phase adjuster and the audio processing circuit, and the first adder is arranged to combine the left channel signal and the first adjusted signal to generate an adjusted left channel signal. The first analog-to-digital converter is coupled to the first adder, and arranged to perform an analog-to-digital conversion upon the adjusted left channel signal to generate a left channel audio signal in the audio signals. The second gain and phase adjuster is coupled to the audio processing circuit, and arranged to adjust a gain and a phase of the left channel signal to generate a second adjusted signal. The second adder is coupled to the second gain and phase adjuster and the audio processing circuit, and the second adder is arranged to combine the right channel signal and the second adjusted signal to generate an adjusted right channel signal. The second analog-to-digital converter is coupled to the second adder, and the second analog-to-digital converter is arranged to perform an analog-to-digital conversion upon the adjusted right channel signal to generate a right channel audio signal in the audio signals. 
     According to another embodiment of the present invention, a signal processing method applied to a headset is provided. The headset includes a left earphone, a right earphone and a microphone. The signal processing method includes: receiving a sound signal from the microphone, and converting the sound signal into a digital input signal; generating a left channel signal and a right channel signal, wherein the left channel signal and the right channel signal are utilized to generate audio signals outputted to the left earphone and the right earphone, respectively; adjusting gains and phases of the left channel signal and the right channel signal, to generate a first adjusted signal; and combining the digital input signal and the first adjusted signal, to generate an adjusted digital input signal. 
     According to another embodiment of the present invention, a signal processing method applied to a headset is provided. The headset includes a left earphone, a right earphone and a microphone. The signal processing method includes: generating a left channel signal and a right channel signal; adjusting a gain and a phase of the right channel signal, to generate a first adjusted signal; combining the left channel signal and the first adjusted signal, to generate an adjusted left channel signal; performing an analog-to-digital conversion upon the left channel signal, to generate a left channel audio signal to the left earphone; adjusting a gain and a phase of the left channel signal, to generate a second adjusted signal; combining the right channel signal and the second adjusted signal, to generate an adjusted right channel signal; and performing an analog-to-digital conversion upon the right channel signal, to generate a right channel audio signal to the right earphone. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating an overall structure of a signal processing circuit applied to a headset according to an embodiment of the present invention. 
         FIG. 2  is a diagram illustrating a signal processing circuit according to an embodiment of the present invention. 
         FIG. 3  is a flowchart illustrating a signal processing method according to an embodiment of the present invention. 
         FIG. 4  is a flowchart illustrating to a signal processing method according to another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Certain terms are used throughout the description and following claims to refer to particular components. As one skilled in the art will appreciate, manufacturers may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following description and in the claims, the terms “include” and “comprise” are used in an open-ended fashion, and thus should be interpreted to mean “include, but not limited to . . . ”. Also, the term “couple” is intended to mean either an indirect or direct electrical connection. Accordingly, if one device is coupled to another device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections. 
     Please refer to  FIG. 1 , which is a diagram illustrating an overall structure of a signal processing circuit  102  applied to a headset  110  according to an embodiment of the present invention. As shown in  FIG. 1 , the signal processing circuit  102  is manufactured in a chip  100 . The chip  100  includes at least four connection points Mic_in, HPO_R, HPO_L and GND_ref connected to four different terminals of a sound jack  130  through layout traces, respectively. Besides, the headset  110  includes a right earphone  112 _R, a left earphone  112 _L, a microphone  114  and an audio plug  116 , wherein the audio plug  116  mainly includes four connection points Mic, Gnd, R and L. 
     When the audio plug  116  is connected to the audio jack  130  and the chip  100  starts operating, sounds recorded by the microphone  114  will be transmitted to the signal processing circuit  102  through the connection point Mic on the audio plug  116  and the connection point Mic_in on the chip  100  (the element R1 show in  FIG. 1  is a resistor), a left channel audio signal generated by the signal processing circuit  102  will be transmitted to the left earphone  112 _L through the connection point HPO_L on the chip  100  and the connection point L on the audio plug  116 , and a right channel audio signal generated by the signal processing circuit  102  will be transmitted to the right earphone  112 _R through the connection point HPO_R on the chip  100  and the connection point R on the audio plug  116 . 
     Further, as shown in  FIG. 1 , since the connection point Gnd (i.e., the grounding point) on the audio plug  116  is connected to the connection point GND_ref (i.e., the reference grounding point) on the chip  100  through a layout trace, the existence of the impedance R2 of the connection point Gnd, the impedance R3 of the layout trace and the impedance R4 of the inner grounding point of the chip  100  makes the grounding voltage value become unstable, which causes the left channel audio signal of the left earphone  112 _L and the right channel audio signal of the right earphone  112 _R to be coupled to other signal line(s). For example, referring to  FIG. 1 , when the chip  100  outputs right channel audio signals from the connection point HPO_R, part of the right channel audio signals will be coupled to the layout trace between the connection point Gnd and the connection point GND_ref, and then these coupling signals will be transmitted to the left earphone  112 _L and the connection point Mic_in of the chip  100 . Consequently, the user hears the right channel audio signals from the left earphone  112 _L. Further, the sounds recorded by the microphone  114  will be mixed with these coupling signals, thus deteriorating the sound recording quality as well as the sound playback quality. 
     Please refer to  FIG. 2 , which is a diagram illustrating a signal processing circuit  102  according to an embodiment of the present invention. As shown in  FIG. 2 , the signal processing circuit  102  includes an audio processing circuit  210 , an analog-to-digital (A/D) converter  220 , three adders  222 ,  232 ,  242 , three gain and phase adjusters  224 ,  230  and  240 , and two digital-to-analog (D/A) converters  250  and  260 . 
     Please refer to both  FIGS. 1 and 2 . In a case where the signal processing circuit  102  simultaneously picks up sounds and plays sounds, the A/D converter  220  receives the sound signal S Mic  from the microphone  114 , and performs the A/D conversion upon the sound signal S Mic  to generate a digital input signal D in . Meanwhile, the left channel signal S L  and the right channel signal R L  are transmitted to the gain and phase adjuster  224 , and then the gain and phase adjuster  224  adjusts the gain and phase of each of the left channel signal S L  and the right channel signal S R  to generate an adjusted signal S a1 . In this embodiment, the gain and phase adjuster  224  may be utilized to generate the adjusted signal S a1  by adjusting the gain and phase of a signal derived from summing up (combining) the left channel signal S L  and the right channel signal R L , or by adjusting the phases and gains of the left channel signal S L  and the right channel signal R L  respectively and then summing up the adjusted left channel signal and the adjusted right channel signal. 
     Further, the settings of the gain and phase adjuster  224  that are related to the gain adjusting amount and the phase adjusting amount may be determined by a designer or a manufacturer referring to experiment results. That is, the gain adjusting amount and the phase adjusting amount may be set by fixed values. Alternatively, the gain adjusting amount and the phase adjusting amount may be dynamically adjusted according to the change/variation of the digital input signal D in ′. The amplitude of the adjusted signal S a1  outputted by the gain and phase adjuster  224  is similar to the amplitude of the coupling signal coupled to the connection point Mic_in as shown in  FIG. 1 , but would have an opposite phase. 
     Then, the adder  222  sums up (combines) the digital input signal D in  and the adjusted signal S a1  to generate an adjusted digital input signal D in ′ to the audio processing circuit  210 . Since the coupling signal included in the digital input signal D in  and the adjusted signal S a1  have the same amplitude but opposite phases, the adjusted digital input signal D in ′ may be viewed as a clean sound signal recorded by the microphone  114 , thus improving the sound recording quality of the microphone  114 . 
     On the other hand, the gain and phase adjuster  230  adjusts the gain and phase of the right channel signal S R  to generate an adjusted signal S a2 . After that, the adder  232  sums up (combines) the left channel signal S L  and the adjusted signal S a2  to generate an adjusted left channel signal S L ′. The adjusted left channel signal S L ′ is converted into a left channel audio signal S LCH  through the D/A converter  250 , and the left channel audio signal S LCH  is transmitted to the left earphone  112 _L through the connection point HPO_L of the chip  100  and the connection point L of the audio plug  116 . 
     Further, the settings of the gain and phase adjuster  230  that are related to the gain adjusting amount and the phase adjusting amount may be determined by a designer or a manufacturer referring to experiment results. That is, the gain adjusting amount and the phase adjusting amount may be set by fixed values. Alternatively, the gain adjusting amount and the phase adjusting amount maybe dynamically adjusted according to the change/variation of the adjusted signal S a2 . The amplitude of the adjusted signal S a2  outputted by the gain and phase adjuster  230  is similar to the amplitude of the coupling signal coupled to the left earphone  112 _L as shown in  FIG. 1 , but would have an opposite phase. 
     The operation of the aforementioned gain and phase adjuster  230  and the adder  232  may be viewed as a pre-adjustment of the left channel signal S L /left channel audio signal S LCH , which makes the sound heard by the user through the left earphone  112 _L similar to the contents of the left channel signal S L  without being interfered with the coupling signal as shown in  FIG. 1 . 
     Similarly, the gain and phase adjuster  240  adjusts the gain and phase of the left channel signal S L  to generate an adjusted signal S a3 . After that, the adder  242  sums up (combines) the right channel signal S R  and the adjusted signal S a3  to generate an adjusted right channel signal S R ′. Then, the adjusted right channel signal S R ′ is converted into a right channel audio signal S RCH  through the D/A converter  260 , and the right channel audio signal S RCH  is transmitted to the right earphone  112 _R through the connection pint HPO_R of the chip  100  and the connection point R of the audio plug  116 . 
     Further, the settings of the gain and phase adjuster  240  that are related to the gain adjusting amount and the phase adjusting amount may be determined by a designer or a manufacturer referring to experiment results. That is, the gain adjusting amount and the phase adjusting amount may be set by fixed values. Alternatively, the gain adjusting amount and the phase adjusting amount maybe dynamically adjusted according to the change of the adjusted signal S a3 . The amplitude of the adjusted signal S a3  outputted by the gain and phase adjuster  240  will be similar to the amplitude of the coupling signal coupled to the right earphone  112 _R as shown in  FIG. 1 , but have an opposite phase. 
     The operation of the aforementioned gain and phase adjuster  240  and the adder  242  may be viewed as a pre-adjustment of the right channel signal S R /right channel audio signal S RCH , which makes the sound heard by the user through the right earphone  112 _R similar to the contents of the right channel S R  without being interfered with the coupling signal. 
     In summary, the signal processing circuit  102  of the present invention is capable of canceling the interference resulting from the coupling signal. Hence, the sound recording quality of the microphone  114  and the sound playback quality of the right earphone  112 _R and the left earphone  112 _L will be greatly improved. 
       FIG. 3  is a flowchart illustrating a signal processing method according to an embodiment of the present invention, wherein the flowchart in  FIG. 3  mainly corresponds to the operations on the audio processing circuit  210 , the A/D converter  200 , the adder  222  and the gain and phase adjuster  224  shown in  FIG. 2 . Please refer to  FIGS. 1-3 . The signal processing method of  FIG. 3  is as follows: 
     Step  300 : Start. 
     Step  302 : Receive a sound signal from a microphone, and convert the sound signal into a digital input signal. 
     Step  304 : Generate a left channel signal and a right channel signal, wherein the left channel signal and the right channel signal are utilized to generate audio signals outputted to the left earphone and the right earphone. 
     Step  306 : Adjust gains and phases of the left channel signal and the right channel signal to generate a first adjusted signal. 
     Step  308 : Combine the digital input signal and the first adjusted signal to generate an adjusted digital input signal to the audio processing circuit. 
     Please refer to  FIG. 4 , which is a flowchart illustrating a signal processing method according to another embodiment of the present invention, wherein the flowchart tin  FIG. 4  mainly corresponds to the operations of the audio processing circuit  210 , the gain and phase adjusters  230 ,  240 , the adders  232 ,  242  and the D/A converters  250 ,  260  shown in  FIG. 2 . Please refer to  FIGS. 1, 2 and 4 . The signal processing method of  FIG. 4  is as follows: 
     Step  400 : Start. 
     Step  402 : Generate a left channel signal and a right channel signal. 
     Step  404 : Adjust a gain and a phase of the right channel signal to generate a first adjusted signal. 
     Step  406 : Combine the left channel signal and the first adjusted signal to generate an adjusted left channel signal. 
     Step  408 : Perform a digital-to-analog conversion upon the adjusted left channel signal to generate a left channel audio signal to the left earphone. 
     Step  410 : Adjust a gain and a phase of the left channel signal to generate a second adjusted signal. 
     Step  412 : Combine the right channel signal and the second adjusted signal to generate an adjusted right channel signal. 
     Step  414 : Perform a digital-to-analog conversion upon the adjusted right channel signal to generate a right channel audio signal to the right earphone. 
     In brief, with the use of the proposed signal processing circuit and signal processing method applied to a headset according to the present invention, when there is impedance existing in the grounding point of the audio jack, the inner grounding point of the audio chip (audio IC), or the layout trace for connecting the audio jack to the audio chip, the crosstalk between the left and right channels will be avoided/mitigated, and the microphone will not simultaneously record the signals played by the earphones. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.