Abstract:
A combo-jack detecting circuit for used in an audio CODEC is provided. The combo-jack detecting circuit comprises a low pass filter, a detecting unit and a switch unit. Without coupling capacitor between an audio apparatus and audio codec, the output direct current voltage of the audio apparatus can be provided by the low pass filter. The switch unit is configured to switch selectively for outputting two voltage signals to the low pass filter sequentially. The low pass filter provides two direct current signals so that the detecting unit determines a jack type of the sounding signal apparatus accordingly. By means of proper design, input buffers in the audio codec can transform a common mode voltage of the audio apparatus into a common mode voltage of the audio codec.

Description:
[0001]    This application claims priority to Taiwan Patent Application No. 101119027 filed on May 28, 2012, which is hereby incorporated by reference in its entirety. 
       CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0002]    Not applicable. 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The present invention relates to a combo-jack detecting circuit for use in an audio codec. More particularly, the combo-jack detecting circuit of the present invention is configured to detect a jack type of a combo-jack. 
         [0005]    2. Descriptions of the Related Art 
         [0006]    Many audio apparatuses currently available in the market need to have a simultaneous audio output and input function (e.g., headsets). Most of the existing audio apparatuses have an audio input jack and an audio output jack, which are originally independent from each other, and then integrated into a single combo-jack for convenience. The combo-jack of such an audio apparatus with four terminals is normally provided with a left-sound channel audio output terminal, a right-sound channel audio output terminal, an audio input terminal and a ground terminal. Only in this way, can the audio apparatus play, via a speaker thereof, a sound signal transmitted from an audio codec and output the received sound signal via the audio input terminal to the audio codec for subsequent processing. 
         [0007]    Accordingly, to meet the aforesaid requirements, the combo-jacks currently available adopt four terminals mostly in the form of TRRS (i.e., a terminal Tip, a terminal Ring 1 , a terminal Ring 2  and a terminal Sleeve). To make a combo-jack downward compatible with a common apparatus (e.g., an earphone) with only an input jack, the terminal Tip and the terminal Ring 1  of the combo-jack are fixedly used as the left-sound channel audio output terminal and the right-sound channel audio output terminal respectively. However, on the other hand, the audio input terminal or the ground terminal of the combo-jack is not mandatorily specified to necessarily correspond to the terminal Ring 2  and the terminal Sleeve, so when a designer of audio systems integrates an audio codec with a combo-jack of an audio apparatus, the audio output terminals, the audio input terminal and the ground terminal of the audio codec usually must be designed to match those of the combo-jack. 
         [0008]    In more detail, when the combo-jack of the audio apparatus uses the terminal Ring 2  as the ground terminal and uses the terminal Sleeve as the audio input terminal, the designer of audio systems must design the circuit of the audio codec correspondingly so that the grounding circuit of the audio codec comes into contact with the terminal Ring 2  while the audio input terminal of the audio codec comes into contact with the terminal Sleeve. Likewise, when the combo-jack of the audio apparatus uses the terminal Ring 2  as the audio input terminal and uses the terminal Sleeve as the ground terminal, the designer of audio systems must design the circuit of the audio codec correspondingly so that the grounding circuit of the audio codec comes into contact with the terminal Sleeve, while the audio input terminal of the audio codec comes into contact with the terminal Ring 2 . 
         [0009]    Thus, when the designer of audio systems manufactures the audio codec, the circuit design of the audio codec will be limited by the jack implementation of the combo-jack of the audio apparatus with which the audio codec is to match. Moreover, on the other hand, when a user desires to use an audio apparatus with a single combo-jack among apparatuses with different audio codecs, the user may fail to obtain the expected effect due to incompatibility between the audio codecs and the combo-jack. 
         [0010]    In view of this, it is important to provide a circuit disposed within an audio codec, which can determine the jack implementation of a combo-jack of an audio apparatus to ensure that different combo-jacks can all operate on the audio codec normally. 
       SUMMARY OF THE INVENTION 
       [0011]    An objective of the present invention is to provide a combo-jack detecting circuit for use in an audio codec, which can detect circuits of combo-jacks of audio apparatuses and determine possible jack implementations of the combo-jacks of the audio apparatuses accordingly so that the combo-jacks of the different audio apparatuses can all operate on the audio codec normally. As a result, the user can operate the audio apparatuses and the audio codec more smoothly. 
         [0012]    To achieve the aforesaid objective, the present invention discloses a combo-jack detecting circuit for use in an audio codec, which connects with an audio apparatus electrically. The audio apparatus comprises a first terminal and a second terminal. The combo-jack detecting circuit comprises a low pass filter, a detecting unit coupled to the low pass filter, and a switch unit. The switch unit is coupled to the first terminal, the second terminal and the low pass filter, and selectively switches to output a first voltage signal of the first terminal and a second voltage signal of the second terminal to the low pass filter in order. The low pass filter receives the first voltage signal and the second voltage signal via the switch unit and provides a first direct current signal of the first voltage signal and a second direct current signal of the second voltage signal respectively. The detecting unit determines a jack type of the audio apparatus according to the first direct current signal and the second direct current signal. 
         [0013]    With the technical features disclosed above, the combo-jack detecting circuit of the present invention can determine a jack type of a combo-jack by switching on two circuits between the combo-jack detecting circuit and the combo-jack and according to peak voltages of direct current signals of the two circuits. The detailed technology and preferred embodiments implemented for the subject invention are described in the following paragraphs accompanying the appended drawings for people skilled in this field to well appreciate the features of the claimed invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a schematic view of a combo-jack detecting circuit according to a first embodiment of the present invention; 
           [0015]      FIG. 2A  is a schematic view of a combo-jack detecting circuit according to a second embodiment of the present invention; 
           [0016]      FIG. 2B  is a schematic view illustrating a circuit connection mode between the combo-jack detecting circuit and an audio apparatus according to the second embodiment of the present invention; 
           [0017]      FIG. 2C  is a schematic view illustrating another circuit connection mode between the combo-jack detecting circuit and the audio apparatus according to the second embodiment of the present invention; and 
           [0018]      FIG. 3  is a schematic view of a combo-jack detecting circuit according to a third embodiment of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0019]    In the following descriptions, the present invention will be explained with reference to embodiments thereof. However, these embodiments are not intended to limit the present invention to any specific environments, applications or particular implementations described in these embodiments. Therefore, the description of these embodiments is only for purpose of illustration rather than to limit the present invention. It shall be appreciated that in the following embodiments and the attached drawings, elements not directly related to the present invention are omitted from depiction; and dimensional relationships among individual elements in the attached drawings are illustrated only for ease of understanding but not to limit the actual scale. 
         [0020]      FIG. 1  illustrates a schematic view of a combo-jack detecting circuit  1  according to a first embodiment of the present invention. The combo-jack detecting circuit  1  is electrically connected with an audio apparatus  3  to detect a jack status of the audio apparatus  3 . The audio apparatus  3  comprises a first terminal  311  and a second terminal  313 . The combo-jack detecting circuit  1  comprises a switch unit  11 , a low pass filter  13 , and a detecting unit  15  coupled to the low pass filter  13 . It shall be firstly appreciated that the combo-jack detecting circuit  1  of the present invention may be disposed in an audio codec rather than being limited to being externally connected to the audio codec; and interactions between the elements will be further elucidated herein below. 
         [0021]    Firstly, as shown, because the jack type of the audio apparatus  3  is unknown, the combo-jack detecting circuit  1  must firstly detect voltages of terminals of the audio apparatus  3  in the current circuit connection mode to confirm the jack type of the audio apparatus  3 . Specifically, as shown in  FIG. 1 , when the audio apparatus  3  is connected to the combo-jack detecting circuit  1  via a jack, the switch unit  11  is externally coupled to the first terminal  311  and the second terminal  313  of the audio apparatus  3 , and the switch unit  11  is internally coupled to the low pass filter  13 . 
         [0022]    With the disposition of the switch unit, the combo-jack detecting circuit  1  can determine the jack type of the audio apparatus  3  by detecting voltages of different terminals between the combo-jack detecting circuit  1  and the audio apparatus  3  when a user uses the audio apparatus  3 . In more detail, the switch unit  11  selectively switches to output a first voltage signal V 1  of the first terminal  311  and a second voltage signal V 2  of the second terminal  313  to the low pass filter  13  in order. Then, the detecting unit  15  can carry out subsequent operations for determining the jack type of the audio apparatus  3 . 
         [0023]    Because the first voltage signal V 1  and the second voltage signal V 2  comprise alternating current voltage signals, the direct current signals of the first voltage signal V 1  and the second voltage signal V 2  may be firstly provided by the low pass filter  13  to increase the determination accuracy. It shall be particularly appreciated that providing the direct current signals by the low pass filter is known in the prior art and, thus, will not be further described herein. 
         [0024]    Furthermore, the low pass filter  13  can receive the first voltage signal V 1  and then filter out a first direct current signal VD 1  of the first voltage signal V 1 . Likewise, the low pass filter  13  can receive the second voltage signal V 2  and then filter out a second direct current signal VD 2  of the second voltage signal V 2 . Thus, the detecting unit  15  can determine the jack type of the audio apparatus  3  according to the first direct current signal VD 1  and the second direct current signal VD 2 . 
         [0025]    In more detail, the detecting unit  15  can determine that the first terminal  311  of the audio apparatus  3  is a signal input terminal and the second terminal  313  is a ground terminal when the value of the first direct current signal VD 1  is greater than the value of the second direct current signal VD 2 . The switch unit  11  further connects the second terminal  313  to the ground according to the determination result of the detecting unit  15 . In this way, the audio apparatus  3  can input the signal to the audio codec properly so that the audio codec carries out subsequent operations. 
         [0026]    Conversely, the detecting unit  15  can determine that the first terminal  311  of the audio apparatus  3  is a ground terminal and the second terminal  313  is a signal input terminal when the value of the first direct current signal VD 1  is smaller than the value of the second direct current signal VD 2 . The switch unit  11  connects the first terminal  311  to the ground according to the determination result of the detecting unit  15 . Likewise, the audio apparatus  3  can also input the signal to the audio codec properly in a different jack connection mode so that the audio codec carries out subsequent operations. 
         [0027]    Next,  FIG. 2A  shows a schematic view of a combo-jack detecting circuit  2  according to a second embodiment of the present invention. The combo-jack detecting circuit  2  is electrically connected with an audio apparatus  4  to detect a jack status of the audio apparatus  4 . The audio apparatus  4  could be at least modeled as a transistor  41  and a sensing capacitor  43  coupled to the transistor  41 . The transistor  41  comprises a first terminal  411  and a second terminal  413 . The first terminal  411  and the second terminal  413  of the audio apparatus  4  are coupled to a stable bias voltage BIAS via a first resistor R 1  and a second resistor R 2  respectively. The audio apparatus  4  is activated mainly by the stable bias voltage BIAS. 
         [0028]    On the other hand, the combo-jack detecting circuit  2  comprises a switch unit  21 , a low pass filter  23 , and a detecting unit  25  coupled to the low pass filter  23 . The switch unit  21  comprises a first switch set and a second switch set. The first switch set comprises a first ground control switch SG 1  and a first detection control switch S 1 . The second switch set comprises a second ground control switch SG 2  and a second detection control switch S 2 . Likewise, the combo-jack detecting circuit  2  of the present invention may be disposed in an audio codec rather than being limited to being externally connected to the audio codec. Interactions between the elements will be further elucidated hereinbelow. 
         [0029]    As shown, because the jack type (i.e., the circuit connection mode between the sensing capacitor  43  and the transistor  41 ) of the audio apparatus  4  is unknown (represented by an unknown circuit and dashed lines), the combo-jack detecting circuit  2  must firstly detect voltages of terminals of the audio apparatus  4  in the current circuit connection mode to confirm the jack type of the audio apparatus  4 . Specifically, as shown in  FIG. 2A , when the audio apparatus  4  is connected to the combo-jack detecting circuit  2  via a jack, the low pass filter  23  is coupled to the first terminal  411  and the second terminal  413  of the transistor  41  via the first detection control switch S 1  and the second detection control switch S 2  respectively, the first ground control switch SG 1  is coupled between the second terminal  413  and a first ground end GN 1 , while the second ground control switch SG 2  is coupled between the first terminal  411  and a second ground end GN 2 . 
         [0030]    With the disposition of the switch unit, the combo-jack detecting circuit  2  can determine the jack type (i.e., the circuit connection mode between the sensing capacitor  43  and the transistor  41 ) of the audio apparatus  4  by detecting voltages of different terminals between the combo-jack detecting circuit  2  and the audio apparatus  4  when the user uses the audio apparatus  4 . In more detail, because the stable bias voltage BIAS is mainly used to activate the audio apparatus  4 , a stable direct current voltage signal can be supplied to the transistor  41  by the stable bias voltage BIAS via the first resistor R 1  when the first ground control switch GN 1  and the first detection control switch S 1  are switched on and the second ground control switch GN 2  and the second detection control switch S 2  are switched off. Meanwhile, when the user uses the audio apparatus  4 , the sensing capacitor  43  also generates voltage variations according to the vibrations of a sound, and supplies an alternating current voltage signal to the transistor  41 . Thus, a first voltage signal V 1  is formed by the stable bias voltage BIAS and the sensing capacitor  43  at the first terminal  411 . 
         [0031]    On the other hand, when the second ground control switch GN 2  and the second detection control switch S 2  are switched on and the first ground control switch GN 1  and the first detection control switch S 1  are switched off, the stable bias voltage BIAS supplies a stable direct current voltage signal to the transistor  41  via the second resistor R 2 . Likewise, when the user uses the audio apparatus  4 , the sensing capacitor  43  also generates voltage variations according to the vibrations of a sound, and supplies an alternating current voltage signal to the transistor  41 . Thus, a second voltage signal V 2  is formed by the stable bias voltage BIAS and the sensing capacitor  43  at the second terminal  413 . 
         [0032]    Then, the detecting unit  25  can carry out subsequent operations for determining the jack type of the audio apparatus  4 . Because the first voltage signal V 1  and the second voltage signal V 2  comprise alternating current voltage signals, the direct current signals of the first voltage signal V 1  and the second voltage signal V 2  may be firstly provided by the low pass filter  23  to increase the determination accuracy. It shall be particularly appreciated that providing the direct current signals by the low pass filter is known in the prior art and, thus, will not be further described herein. 
         [0033]    Furthermore, when the first voltage signal V 1  is formed by the stable bias voltage BIAS and the sensing capacitor  43  at the first terminal  411 , the low pass filter  23  can receive the first voltage signal V 1  via the first detection control switch S 1  that is switched on, and then provide a first direct current signal VD 1  of the first voltage signal V 1 . Likewise, when the second voltage signal V 2  is formed by the stable bias voltage BIAS and the sensing capacitor  43  at the second terminal  413 , the low pass filter  13  can receive the second voltage signal V 2  via the second detection control switch S 2  that is switched on, and then provide a second direct current signal VD 2  of the second voltage signal V 2 . 
         [0034]    Then, the detecting unit  25  can detect a first peak voltage (not shown) of the first direct current signal VD 1  and second peak voltage (not shown) of the second direct current signal VD 2 , and determine the jack type of the audio apparatus  4  according to the first peak voltage and the second peak voltage. Thus, the detecting unit  25  can reduce the instability caused by the alternating current signals to increase the determination accuracy. 
         [0035]      FIG. 2B  illustrates a schematic view of a circuit connection mode between the combo-jack detecting circuit  2  and the audio apparatus  4  according to the second embodiment of the present invention. It shall be firstly particularly appreciated that when the circuit of the audio apparatus  4  is as shown in  FIG. 2B  in which two terminals of the sensing capacitor  43  are connected to a gate and the second terminal  413  of the transistor  41  respectively, the correct circuit between the audio apparatus  4  and the stable bias voltage BIAS shall be that the stable bias voltage BIAS inputs the direct current voltage signal to the transistor  41  from the first terminal  411  via the first resistor R 1  and the second terminal  413  of the transistor  41  is connected to the first ground end GN 1 . In this case, the first peak voltage of the first direct current signal VD 1  will be greater than the second peak voltage of the second direct current signal VD 2  in this normal circuit connection mode. 
         [0036]    In other words, when the detecting unit  25  detects that the first peak voltage of the first direct current signal VD 1  is greater than the second peak voltage of the second direct current signal VD 2  through what is described in the aforesaid embodiment, the detecting unit  25  can determine that the circuit of the audio apparatus  4  shall be as shown in  FIG. 2B  (i.e., the first terminal  411  of the transistor  41  is connected to the stable bias voltage BIAS via the first resistor R 1 , and the second terminal  413  of the transistor  41  is connected to the first ground end GN 1 ). Accordingly, the switch unit  21  can further connect the second terminal  413  to the ground (i.e., have the first ground control switch SG 1  switched on and the second ground control switch SG 2  switched off) according to the determination result of the detecting unit  25  so that the audio codec processes the first voltage signal V 1  as the primary signal source. 
         [0037]    Similarly,  FIG. 2C  illustrates a schematic view of another circuit connection mode between the combo-jack detecting circuit  2  and the audio apparatus  4  according to the second embodiment of the present invention. Likewise, when the circuit of the audio apparatus  4  is as shown in  FIG. 2C  in which two terminals of the sensing capacitor  43  are connected to a gate and the first terminal  411  of the transistor  41  respectively, the correct circuit between the audio apparatus  4  and the stable bias voltage BIAS shall be that the stable bias voltage BIAS inputs the direct current voltage signal to the transistor  41  from the second terminal  413  via the second resistor R 2  and the first terminal  411  of the transistor  41  is connected to the second ground end GN 2 . In this case, the second peak voltage of the second direct current signal VD 2  will be greater than the first peak voltage of the first direct current signal VD 1  in this normal circuit connection mode. 
         [0038]    In other words, when the detecting unit  25  detects that the second peak voltage of the second direct current signal VD 2  is greater than the first peak voltage of the first direct current signal VD 1  through what is described in the aforesaid embodiment, the detecting unit  25  can determine that the circuit of the audio apparatus  4  shall be as shown in  FIG. 2C  (i.e., the second terminal  413  of the transistor  41  is connected to the stable bias voltage BIAS via the second resistor R 2 , and the first terminal  411  of the transistor  41  is connected to the second ground end GN 2 ). Accordingly, the switch unit  21  can further connect the first terminal  411  to the ground (i.e., with the second ground control switch SG 2  switched on and the first ground control switch SG 1  switched off) according to the determination result of the detecting unit  25  so that the audio codec processes the second voltage signal V 2  as the primary signal source. 
         [0039]    Next,  FIG. 3  illustrates a schematic view of a combo-jack detecting circuit  2 ′ according to a third embodiment of the present invention. The combo-jack detecting circuit  2 ′ further comprises a capacitor pin  26 , a first stage buffer  27  and a second stage buffer  29 . The first stage buffer  27  has a first input terminal  271 , a second input terminal  272 , a first output terminal  273  and a second output terminal  274 . The second stage buffer  29  is coupled to a common mode contact VCM, and has a first input terminal  291 , a second input terminal  292 , a first output terminal  293  and a second output terminal  294 . It shall be particularly appreciated that elements with the same designations in the third embodiment and the second embodiment have similar functions and, thus, will not be further described herein. However, the third embodiment will focus on the functions of the capacitor pin and the two stage buffers. 
         [0040]    Specifically, the function of the capacitor pin  26  is to enhance the direct current signal filtering effect of the low pass filter  23 . Furthermore, when the capacitor pin  26  is coupled between the low pass filter  23  and the detecting unit  25  and electrically connected to an external capacitor  5  (which may be a capacitor with a large capacitance), the direct current signal filtering effect of the low pass filter  23  can be further enhanced to ensure that the determination result of the detecting unit  25  is correct and, at the same time, the filtered direct current signal is transmitted to the buffers. 
         [0041]    On the other hand, the stable bias voltage BIAS for activating the audio apparatus  4  and the direct current signal obtained by the audio apparatus  4  may be different from the direct current operating voltage in the audio codec, and this will cause the audio codec to be prone to errors during subsequent coding/decoding operations. Accordingly, before a signal is inputted to the audio codec, the signal must be properly processed by the buffers to adjust an operating voltage of the signal to be identical to the operating voltage of the audio codec. Specifically, in the case in which the first voltage signal V 1  is used as the primary signal source as an example, the first input terminal  271  is coupled between the switch unit  21  and the low pass filter  23  to receive the first voltage signal V 1  directly, and the second input terminal  272  is coupled between the low pass filter  23  and the detecting unit  25  to receive the first direct current signal VD 1 . 
         [0042]    In this case, the first stage buffer  27  can convert the inputted first voltage signal V 1  (comprising the first direct current signal VD 1 ) and the inputted first direct current signal VD 1  into a first alternating current signal A 1  and a second alternating current signal A 2  corresponding to the first voltage signal V 1  and the first direct current signal VD 1  (i.e., the first alternating current signal A 1  and the second alternating current signal A 2  with a first direct current signal level), and output the first alternating current signal A 1  and the second alternating current signal A 2  via the first output terminal  273  and the second output terminal  274  respectively. Phases of the first alternating current signal A 1  and the second alternating current signal A 2  are opposite. 
         [0043]    Then, the first input terminal  291  coupled to the first output terminal  273  receives the first alternating current signal A 1 , and the second input terminal  292  coupled to the second output terminal  274  receives the second alternating current signal A 2 . Accordingly, the second stage buffer  29  can, on the basis of a common mode voltage signal (not shown) of the common mode contact VCM, convert the inputted first alternating current signal A 1  and the inputted second alternating current signal A 2  into a third alternating current signal A 3  and a fourth alternating current signal A 4  which are based on a level of the common mode voltage signal, and output the third alternating current signal A 3  and the fourth alternating current signal A 4  via the first output terminal  293  and the second output terminal  294  respectively. Phases of the third alternating current signal A 3  and the fourth alternating current signal A 4  are opposite. Thus, the signal source (i.e., the third alternating current signal A 3  and the fourth alternating current signal A 4 ) of the audio codec is signals based on the level of the common mode voltage signal, so the subsequent coding/decoding operations can be carried out normally. 
         [0044]    On the other hand, in the case in which the second voltage V 2  is used as the primary signal source as an example, the first input terminal  271  is coupled between the switch unit  21  and the low pass filter  23  to receive the second voltage V 2  directly, and the second input terminal  272  is coupled between the low pass filter  23  and the detecting unit  25  to receive the second direct current signal VD 2 . In this case, the first stage buffer  27  can convert the inputted second voltage V 2  (comprising the second direct current signal VD 2 ) and the inputted second direct current signal VD 2  into a first alternating current signal A 1 ′ and a second alternating current signal A 2 ′ corresponding to the second voltage V 2  and the second direct current signal VD 2  (i.e., the first alternating current signal A 1 ′ and the second alternating current signal A 2 ′ have a second direct current signal level), and output the first alternating current signal A 1 ′ and the second alternating current signal A 2 ′ via the first output terminal  273  and the second output terminal  274  respectively. Phases of the first alternating current signal A 1 ′ and the second alternating current signal A 2 ′ are opposite. 
         [0045]    Then, the first input terminal  291  coupled to the first output terminal  273  receives the first alternating current signal A 1 ′, and the second input terminal  292  coupled to the second output terminal  274  receives the second alternating current signal A 2 ′. Accordingly, the second stage buffer  29  can also, on the basis of a common mode voltage signal of the common mode contact VCM, convert the inputted first alternating current signal A 1 ′ and the inputted second alternating current signal A 2 ′ into a third alternating current signal A 3 ′ and a fourth alternating current signal A 4 ′ which are based on a level of the common mode voltage signal, and output the third alternating current signal A 3 ′ and the fourth alternating current signal A 4 ′ via the first output terminal  293  and the second output terminal  294  respectively. Phases of the third alternating current signal A 3 ′ and the fourth alternating current signal A 4 ′ are opposite. Thus, the signal source (i.e., the third alternating current signal A 3 ′ and the fourth alternating current signal A 4 ′) of the audio codec is a signal based on the level of the common mode voltage signal, so the subsequent coding/decoding operations can be carried out normally. 
         [0046]    According to the above descriptions, the combo-jack detecting circuit of the present invention can detect circuits of combo-jacks of audio apparatuses and determine possible jack implementations of the combo-jacks of the audio apparatuses accordingly so that the combo-jacks of the different audio apparatuses can all operate on the audio codec normally and thus, the user can operate the audio apparatuses and the audio codec more smoothly. 
         [0047]    The above disclosure is related to the detailed technical contents and inventive features thereof. People skilled in this field may proceed with a variety of modifications and replacements based on the disclosures and suggestions of the invention as described without departing from the characteristics thereof. Nevertheless, although such modifications and replacements are not fully disclosed in the above descriptions, they have substantially been covered in the following claims as appended.