Patent Publication Number: US-2011054651-A1

Title: Audio input unit

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to electronic devices and, particularly, to an audio input unit. 
     2. Description of Related Art 
     In general, portable electronic devices such as mobile phones, media players, digital cameras often have an audio input unit. The audio input unit includes an audio capturing unit, a codec, and an input circuit connected between the audio capturing unit and the codec. Usually, the quality of the audio input unit is determined by the audio capturing unit, the codec, and the input circuit. However, high quality audio capturing unit and codec are expensive, which largely add to the cost of the audio input unit. 
     Therefore, an audio input unit is desired to overcome the above-described limitations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the audio input unit. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views 
         FIG. 1  is a block diagram of an audio input unit, in accordance with an embodiment. 
         FIG. 2  is a circuit diagram of the audio input unit of  FIG. 1 , in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , an audio input unit  1  includes an audio [F1]  capturing unit  10 , an input circuit  21 , and a codec  60 . The input circuit  21  includes a first coupling circuit  20 , a signal filtering circuit  30 , a second coupling circuit  40 , and a converting circuit  50 . The audio capturing unit  10 , the first coupling circuit  20 , the signal filtering circuit  30 , the second coupling circuit  40 , the converting circuit  50 , and the codec  60 , are connected in series in that order. 
     The audio capturing unit  10  is used for capturing audio when turned on and converting the audio into electronic signals. The electronic signals include direct-current signals, first harmonic alternating current signals, second harmonic alternating current signals, third harmonic alternating current signals and other high harmonic alternating current signals. The audio capturing unit  10  can be a microphone, or the like. The first coupling circuit  20  is used for filtering most of direct-current signals of electronic signals from the audio capturing unit  10 . The signal filtering circuit  30  is used for filtering out noise of the electronic signals. The noise includes second harmonic, third harmonic, and other high harmonic alternating current signals. The second coupling circuit  40  is used for filtering direct-current signals of electronic signals from the signal filtering circuit  30 , then further filtering the direct-current signals of the electronic signals. 
     The converting circuit  50 , includes an input port  501 , a first output port  502 , and a second output port  503 . The input port  501  is connected to the second coupling circuit  40 . The first output port  502  is connected to a positive terminal of the codec  60 , while the second output port  503  is connected to a negative terminal of the codec  60 . When the input port  501  of the converting circuit  50  receives the filtered electronic signal from the second coupling circuit  40 , the first output port  502  outputs a signal with the same phase as the filtered electronic signal, the second output port  503  outputs a signal with the reverse phase as the filtered electronic signal. The two output signals have the opposite phase and the same amplitude. Then the two signals inputted to the positive terminal and negative terminal of the codec  60  are differential signals having the opposite phase and the same amplitude. Signal-to-Noise and sensitivity of the signals which inputted to the codec  60  are improved. 
     The audio input unit  1  further includes a power supply circuit  70  used for supplying power to the audio input unit  1 . 
     Referring to  FIG. 2 , the power supply circuit  70  includes a power pin [F2]   701  and a power filtering circuit  702 . The power pin  701  is used for connecting to external power source. The power filtering circuit  702  is used for filtering the power obtained by the power pin  701 , which includes a first RC low-pass filter and a pull down resistor R 8 . The first RC low-pass filter includes a resistor R 7  and a capacitor C 6 . A terminal of the pull down resistor R 8  is connected to the output port  7021  of the first RC low-pass filter, the other terminal of the pull down resistor R 8  is connected to the positive pole of the audio capturing unit  10 . When the power pin  701  connects to the external power source, the voltage provided by the external power source is provided to the audio capturing unit  10  after being filtered by the first RC low-pass filter and pulled down by the pull down resistor R 8 . In the exemplary embodiment, the audio capturing unit  10  is a condenser electret microphone, which captures audio and converts the audio into electronic signals, the negative pole of the microphone is connected to ground, the positive pole is connected to the first coupling circuit  20 . 
     In the circuit, the first coupling circuit  20  includes a capacitor C 1  to block most of direct current signals while allowing alternating current signals to pass. 
     The signal filtering circuit  30  includes a second RC low-pass filter, and a resister R 2 . The second RC low-pass filter includes a resistor R 1  and a capacitor C 2 . The resister R 2  and the capacitor C 2  are connected in parallel. The signal filtering circuit  30  is used for filtering out noise of the electronic signals from the first coupling circuit  20 , for example, the signal filtering circuit  30  filters out high harmonics and other noise of the electronic signals. 
     The second coupling circuit  40  includes a capacitor C 3 . One end of the capacitor C 3  is connected to the signal filtering circuit  30 . The capacitor C 3  further blocks direct-current signals of the electronic signals. 
     The converting circuit  50  includes a transistor Q 1 , a first capacitor C 4 , and a second capacitor C 5 . The base of the transistor Q 1  is connected to the other end of the capacitor C 3 , and is connected to the power pin  701  via a first resistor R 3 . The base is connected to ground via a second resistor R 4 . The emitter of the transistor Q 1  is connected to a first terminal of the first capacitor C 4 , the emitter of the transistor Q 1  is further connected to ground via a third resistor R 6 . The collector of the transistor Q 1  is connected to a first terminal of the second capacitor C 5 , the collector of the transistor Q 1  is further connected to the power pin  701  via a fourth resistor R 5 . 
     The base of the transistor Q 1  serves as the input port  501  of the converting circuit  50  A second terminal of the first capacitor C 4  serves as the first output port  502  of the converting circuit  50  and is connected to the positive terminal of the codec  60 . A second terminal of the second capacitor C 5  serves as the second output port  503  of the converting circuit  50  and is connected to the negative terminal of the codec  60 . In the converting circuit  50 , the electronic signals will add the direct-current signals from the transistor Q 1 . The direct-current signals from the transistor Q 1  affects Signal-to-Noise and sensitivity of the electronic signals. The first capacitor C 4  and the second capacitor C 5  are thus used for filtering direct-current signals of the electronic signals output from the emitter and the collector of the transistor Q 1 . 
     When the input port  501  of the converting circuit  50  receives filtered electronic signals from the second coupling circuit  40 , the first output port  502  outputs a signal with the same phase as the filtered electronic signal, the second output port  503  outputs a signal with the reverse phase as the filtered electronic signal, the two output signals have opposite phase and the same amplitude and are input to the positive terminal and negative terminal of the codec  60 . Signal-to-Noise and sensitivity of signals input to the codec  60  are improved. Thus, quality of the audio input unit  1  is improved accordingly. 
     Although the present disclosure has been specifically described on the basis of the exemplary embodiment thereof, the disclosure is not to be construed as being limited thereto. Various changes or modifications may be made to the embodiment without departing from the scope and spirit of the disclosure.