Abstract:
The invention provides a signal transmission apparatus and a signal recording apparatus by which, while a rotary transformer is used, a wide bandwidth and a high transfer rate can be used without a significant increase of the cost or a bad influence on signal recording. A rotary transformer is interposed between a transmission side circuit and a reception side circuit. A passive element circuit including an inductance element is connected to an input stage, that is, the stator side, of the rotary transformer in parallel to the rotary transformer. The passive element circuit has an inductance value set equal to or lower than an equivalent inductance value when the circuit of the rotary transformer side is viewed from the transmission side circuit to achieve impedance matching.

Description:
RELATED APPLICATION DATA 
     The present application claims priority to Japanese Application(s) No.(s). P2001-236237 filed Aug. 3, 2001, which application(s) is/are incorporated herein by reference to the extent permitted by law. 
     BACKGROUND OF THE INVENTION 
     This invention relates to a technique for allowing a wide band and a high transfer rate to be used and improving a rising characteristic of recording current to reduce the error rate in a signal transmission apparatus and a signal recording apparatus in which a rotary transformer is used. 
     An apparatus is known that uses a rotary transformer as signal transmission means for transmitting a signal to a rotary system. For example, in a magnetic recording and/or reproduction apparatus in which a rotary head is used, a rotary transformer is used in a circuit which transmits a signal from a drive circuit, which controls recording current, to the rotor side of the recording head. 
     It is already known that the frequency characteristic of the circuit of the type mentioned depends upon such various factors as the capacitance of active elements such as transistors of an IC (integrated circuit), wiring lines and so forth which form the drive circuit, the inductance, coupling coefficient and floating capacitance relating to the rotary transformer, and the inductance and the capacitance of the head. 
     Incidentally, if it is attempted to increase the bandwidth and the transfer rate in such a conventional circuit as described, then, for example, such countermeasures as listed below are taken: 
     (A) To reduce the capacitance; 
     (B) To raise the coupling coefficient of the transformer; and 
     (C) To reduce the inductance of the head and/or the rotary transformer. 
     However, the countermeasure (A) is impractical because the capacitance relies almost upon the devices used and therefore there remains little room for improvement. 
     Meanwhile, the countermeasure (B) gives rise to a problem of, for example, a drawback that raising of the coupling coefficient increases the cost upon mass production. 
     Further, the countermeasure (C) has a fixed limit because the reduction of the inductance gives rise to problems of increase of recording current, drop of the recording efficiency and so forth. 
     Accordingly, even if trial and error is repeated combining the countermeasures mentioned above suitably, it is difficult to achieve a sufficient transmission characteristic or recording characteristic. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a signal transmission apparatus and a signal recording apparatus using a rotary transformer, which is capable of using a wide bandwidth and a high transfer rate, without a significant increase of the cost or a bad influence on signal recording. 
     In order to attain the object described above, according to an aspect of the present invention, there is provided a signal transmission apparatus in which a rotary transformer is used, including a transmission side circuit including a drive circuit and a reception side circuit including a load, the rotary transformer being interposed between the transmission side circuit and the reception side circuit, and a passive element circuit including an inductance element and connected to an input stage of the rotary transformer in parallel to the rotary transformer, the passive element circuit having an inductance value set equal to or lower than an equivalent inductance value when the circuit of the rotary transformer side is viewed from the transmission side circuit. 
     With the signal transmission apparatus, only by providing a passive element circuit including an inductance element at the input stage of the rotary transformer, the bandwidth and the transmission efficiency can be improved without involving a significant increase of the cost. 
     According to another aspect of the present invention, there is provided a signal recording apparatus in which a rotary transformer is used, including a transmission side circuit and a reception side circuit between which the rotary transformer is interposed, the transmission side circuit being provided on the stator side of the rotary transformer while the reception side circuit is provided on the rotor side of the rotary transformer, the transmission side circuit including a recording circuit while the reception side circuit includes a recording head or a recording head and a reproduction amplifier such that an output signal of the recording circuit is transmitted to the recording head of the reception side circuit through the rotary transformer, and a passive element circuit including an inductance element and connected to an input stage of the rotary transformer in parallel to the rotary transformer, the passive element circuit having an inductance value set equal to or lower than an equivalent inductance value when the circuit of the rotary transformer side is viewed from the transmission side circuit. 
     With the signal recording apparatus, the recording bandwidth is expanded when compared with that of a conventional signal recording apparatus. Consequently, improvement in error rate, that is, reduction of the error rate, by an effect of improvement of the recording signal waveform can be achieved, and therefore, higher density recording can be anticipated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects of the invention will be seen by reference to the description, taken in connection with the accompanying drawing, in which: 
     FIG. 1 is a circuit diagram showing a configuration of a signal transmission apparatus to which the present invention is applied; 
     FIG. 2 is a diagram illustrating an example of magnitude and phase characteristics of the signal transmission apparatus of FIG. 1 where a circuit including an inductor and a resistor connected in series is provided at an input stage of a rotary transformer; 
     FIG. 3 is a diagram illustrating an example of magnitude and phase characteristics of the signal transmission apparatus of FIG. 1 where a circuit including an inductor and a resistor connected in parallel is provided at the input stage of the rotary transformer; 
     FIG. 4 is a diagram illustrating another example of magnitude and phase characteristics of the signal transmission apparatus of FIG. 1 where a circuit including an inductor and a resistor connected in parallel is provided at the input stage of the rotary transformer, but the inductor has a lower inductance value than that in the case of FIG. 3; 
     FIG. 5 is a diagram illustrating, as a comparative example, a further example of magnitude and phase characteristics of the signal transmission apparatus of FIG. 1 where a circuit including an inductor and a resistor connected in parallel is provided at the input stage of the rotary transformer, but the inductor has a higher inductance value than that in the case of FIG. 3; 
     FIG. 6 is a diagram illustrating an example of magnitude and phase characteristics of the signal transmission apparatus of FIG. 1 where a circuit including an inductor and a resistor connected in series and another inductor connected in parallel to the series circuit is provided at the input stage of the rotary transformer; 
     FIG. 7 is a diagram illustrating a circuit characteristic of the signal transmission apparatus of FIG. 1 where it has a certain form in comparison with a characteristic of a conventional circuit; 
     FIG. 8 is a circuit diagram showing a configuration of another signal transmission apparatus to which the present invention is applied; and 
     FIG. 9 is a diagram illustrating a circuit characteristic of the signal transmission apparatus of FIG. 8 where it has another form in comparison with another characteristic of another conventional circuit. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring first to FIG. 1, there is shown a configuration of a signal transmission apparatus to which the present invention is applied. The signal transmission apparatus  1  includes a transmission side circuit  2  and a reception side circuit  3  connected (that is, electro-magnetically coupled) to each other by a rotary transformer  4 . 
     It is to be noted that a rotary transformer is used typically, for example, in a magnetic recording and/or reproduction apparatus using a rotary head. Thus, the signal transmission apparatus  1  shown in FIG. 1 forms as a circuit of a signal recording system of a magnetic recording and/or reproduction apparatus. Further, in the signal transmission apparatus shown in FIG. 1, a rotary transformer with a center tap is used as the rotary transformer  4 . 
     The transmission side circuit  2  includes a drive circuit  5  for providing recording current. In the signal transmission apparatus  1  shown, a current driving IC is used as the drive circuit  5 . The drive circuit  5  of the IC includes a driving amplifier  5   a  to input a recording signal SIG_IN (indicated by a symbol of an ac source in FIG. 1) from a signal processing circuit not shown. The driving amplifier  5   a  has two output terminals connected to the emitters of NPN transistors Q 1  and Q 2  form a differential pair  6  outside the IC. A predetermined voltage from a voltage production section  5   b  (indicated by a symbol of a constant voltage source in FIG. 1) in the IC is supplied to the bases of the transistors Q 1  and Q 2 . The signals obtained at the output terminals of the driving amplifier  5   a  have phases opposite to each other (a round mark (∘) in FIG. 1 represents one of the output terminals), and consequently, the transistors Q 1  and Q 2  are controlled between on and off reciprocally to each other such that, when one of the transistors Q 1  and Q 2  exhibits an on state, the other exhibits an off state. 
     A constant current source “Is” formed using a transistor or the like is externally connected to the current driving IC for controlling the recording current. The current of the driving amplifier  5   a  is controlled through adjustment and setting of the current value of the constant current source Is. 
     The collector of the transistor Q 1  is connected to one end of a winding  4   p  of the primary side (with reference to a transmission direction of a recording signal) of the rotary transformer  4 , and the other end of the winding  4   p  is connected to the collector of the transistor Q 2 . A predetermined voltage “Vcc” from a power supply circuit not shown is supplied to the center tap of the rotary transformer  4  through a power supply terminal TB. Consequently, if the transistor Q 1  is placed into an on state while the transistor Q 2  is placed into an off state, then current flows from the center tap of the winding  4   p  through the winding  4   p  (an upper half portion in FIG. 1) to the transistor Q 1 . On the other hand, if the transistor Q 2  is placed into an on state while the transistor Q 1  is placed into an off state, then current flows from the center tap through the winding  4   p  (a lower half portion in FIG. 1) to the transistor Q 2 . 
     A resistor R 2  is provided at the input stage (stator side) of the rotary transformer  4  and serves as a damping resistor. One end of the resistor R 2  is connected to one end of the winding  4   p  while the other end of the resistor R 2  is connected to the other end of the winding  4   p.    
     The reception side circuit  3  provided on the rotor side of the rotary transformer  4  includes a recording head as a load. The reception side circuit  3  may have a circuit configuration which that includes a recording head, another circuit configuration that includes a recording head and a recording amplifier, a further circuit configuration that includes a recording head, a recording amplifier and a drive circuit, or some other circuit configuration. However, in this embodiment, the reception side circuit  3  shows the simplest configuration including only a recording head  7 . One end of the recording head  7  is connected to one end of a secondary side winding  4   s  of the rotary transformer  4 , and the other end of the recording head  7  is connected to the other end of the secondary side winding  4   s . Further, similar effects are achieved also where a reproduction signal is transmitted to the stator side using a reproduction amplifier of a magneto-resistance (MR) element or a gigantic magneto-resistance (GMR) on the rotor side as a drive circuit. 
     A passive element circuit  8  including an inductance element is provided at the input stage of the rotary transformer  4  of the signal transmission apparatus  1  having the configuration described above. In particular, the passive element circuit  8  including an inductance element (inductor) is connected at the input stage of rotary transformer  4  in a parallel connection relationship to the winding  4   p  of the rotary transformer  4 . The passive element circuit  8  has an inductance value substantially equal to or lower than an equivalent inductance (denoted by “L” in FIG. 1) when the circuit following the rotary transformer is viewed from the transmission side circuit  2 , that is, from the stator side. It is to be noted that the rotary transformer  4  can be approximated to a T equivalent circuit, and the recording head  7  can be replaced substantially with an inductor, a dc resistor and a winding capacitor. Therefore, a circuit simulation can be performed taking a floating capacitance and so forth into consideration. 
     The configuration of the passive element circuit  8  may be a configuration wherein a combination of an inductance element and a resistance element is used as a basic element, another configuration wherein only an inductance element is connected in parallel to the rotary transformer, or a further configuration wherein the two configurations described above are combined with each other such as, for example, those described below. 
     (I) A configuration wherein a circuit including an inductance element L 1  and a resistor R 1  connected in series is used; 
     (II) Another configuration wherein an inductance element L 2  and a resistor R 2  are used; 
     (III) A further configuration wherein a circuit including an inductance element L 1  and a resistor R 1  connected in series and another resistor R 2  connected in parallel to the series circuit are used; and 
     (IV) A still further configuration wherein a circuit including an inductance element L 1  and a resistor R 1  connected in series and another inductance element L 2  or an inductance element L 2  and another resistor R 2  connected in parallel to the series circuit are used. 
     It is to be noted that FIG. 1 shows all of the configurations (I) to (IV) described above in a collected form and therefore shows the configuration (IV) which is a combination of the configurations (I) and (II). 
     First, in the configuration (I), the series circuit of the inductance element L 1  and the resistor R 1  is provided at the input stage of the rotary transformer  4 . Thus, the configuration (I) corresponds to the configuration of the signal transmission apparatus  1  of FIG. 1 that lacks the inductance element L 2  and the resistor R 2 . In this instance, the inductance value of the inductance element L 1  is set substantially equal to the value of the equivalent inductance L including the recording head  7  as a load as viewed from the stator side. Since the bandwidth is widened to the higher frequency side due to an effect of improvement in impedance matching, also higher frequency components than those in the conventional circuit can be transmitted. 
     It is to be noted that, although the signal transmission apparatus  1  in FIG. 1 includes the single series circuit of the inductance element L 1  and the resistor R 1 , it can be formed in various modified forms such as, for example, a form wherein a plurality of such series circuits are connected in parallel. 
     In the configuration (II), the passive element circuit  8  includes only the inductance element L 2  and the resistor R 2  in FIG.  1 . With the configuration (II), a wider band than that of the configuration (I) can be used. However, since the transmission efficiency is deteriorated for the inductance of the inductance element L 2 , it is necessary to take the allowance for loss of the equivalent inductance L into consideration. For example, even if the inductance value of the inductance element L 2  is set to three times the equivalent inductance L, the effect described above still remains. 
     In the configuration (III), the inductance element L 2  is connected in parallel to the series circuit of the inductance element L 1  and the resistor R 1 . Accordingly, the configuration (III) is effective where it is desired to adjust the peak of the frequency characteristic in the configuration (I). 
     The configuration (IV) has a configuration wherein, for example, the inductance element L 1  and the resistor R 1  of the configuration (I) and the inductance element L 2  and the resistor R 2  of the configuration (II) are connected in parallel as shown in FIG.  1 . Accordingly, the configuration (IV) exhibits the effects exhibited by both of the configurations (I) and (II). 
     It is to be noted that the configurations described above are mere possible examples of the configuration of the signal transmission apparatus  1 , and in order to make the frequency characteristic appropriate, naturally such a suitable modification that, for example, a suitable element such as a series circuit of an inductor and a resistor or a resistor is connected additionally to the passive element circuit  8  may be applied to the configurations. 
     FIGS. 2 to  5  show several examples of magnitude and phase characteristics. In FIGS. 2 to  5 , the axis of abscissa indicates the frequency (unit: MHz) and the axis of ordinate indicates the magnitude level (dB) and the phase (°) 
     FIG. 2 shows an example of the characteristics regarding the configuration (I) described above. In FIG. 2, a curve gal indicates a magnitude characteristic and another curve gp 1  indicates a phase characteristic. It is to be noted that the inductance of the inductance element L 1  is set to a value lower than the equivalent inductance L relating to the rotary transformer  4 . 
     FIG. 3 shows an example of the characteristics regarding the configuration (II) described above. In FIG. 3, a curve ga 2  indicates a magnitude characteristic and another curve gp 2  indicates a phase characteristic. It is to be noted that the inductance of the inductance element L 2  is set to a value substantially equal to the equivalent inductance L relating to the rotary transformer  4 . 
     FIG. 4 shows an example of the characteristics regarding the configuration (II) described above. In FIG. 3, a curve ga 3  indicates a magnitude characteristic and another curve gp 3  indicates a phase characteristic. It is to be noted that the inductance of the inductance element L 2  is set to a value lower than the equivalent inductance L relating to the rotary transformer  4 . 
     FIG. 5 shows an example of the characteristics regarding the configuration (II) described above. In FIG. 5, a curve ga 4  indicates a magnitude characteristic and another curve gp 4  indicates a phase characteristic. It is to be noted that the inductance of the inductance element L 2  is set to a value higher by ten times than the equivalent inductance L relating to the rotary transformer  4 . Consequently, the characteristics are almost similar to those of the conventional circuit. Thus, the characteristics are presented as a comparative example. 
     From comparison among the characteristics of FIGS. 3 to  5 , an influence of the relationship in magnitude between the inductance of the inductance element L 2  and the equivalent inductance L described hereinabove can be seen apparently. Where the inductance of the inductance element L 2  is excessively high with respect to the equivalent inductance L, the effect of improvement of the characteristics disappears. 
     FIG. 6 shows an example of the characteristics regarding the configuration (IV) described above. In FIG. 6, a curve ga 5  indicates a magnitude characteristic and another curve gp 5  indicates a phase characteristic. It can be seen that the frequency characteristics are improved significantly with the configuration (IV). It is to be noted that, in this instance, a circuit wherein the inductance element L 2  is connected in parallel to the series circuit of the inductance element L 1  and the resistor R 1  is used. 
     FIG. 7 illustrates an example of an output characteristic of the configuration (IV) in comparison with that of the conventional signal transmission apparatus. In FIG. 7, the axis of abscissa indicates the frequency (unit: MHz) and the axis of ordinate indicates the magnitude level (unit: dB). 
     In FIG. 7, a curve G 1  indicated by a solid line indicates a characteristic of the circuit according to the present invention, and a curve g 1  indicated by an alternate long and two short dashes line indicates a characteristic of the conventional circuit (the configuration of FIG. 1 in which only the resistor R 2  is provided). From comparison between the curves G 1  and g 1 , it can be seen that the characteristic indicated by the curve G 1  extends to the higher frequency side. 
     FIG. 8 shows a configuration of another signal transmission apparatus to which the present invention is applied. Referring to FIG. 8, the signal transmission apparatus  1 A is similar to the signal transmission apparatus  1  in that a transmission side circuit  2  and a reception side circuit  3  are connected to each other using a rotary transformer, but is different in that a rotary transformer having no center tap is used as the rotary transformer. Therefore, the difference of the signal transmission apparatus  1 A from the signal transmission apparatus  1  is described in detail while description of common elements of the signal transmission apparatus  1 A to which like reference characters to those of the signal transmission apparatus  1  are applied is omitted to avoid redundancy. 
     In the signal transmission apparatus  1 A, a circuit section  9  including an inductor LL 1  and a resistor RR 1  connected in parallel and another circuit section  10  including an inductor LL 2  and a resistor RR 2  connected in parallel are connected to a power supply terminal TB. 
     A winding  4   p  of the primary side of the rotary transformer  4 A is connected at one end thereof to the power supply terminal TB through the circuit section  9  and the collector of a transistor Q 1 . The other end of the winding  4   p  is connected to the power supply terminal TB through the circuit section  10  and the collector of another transistor Q 2 . 
     The configurations of the transistors Q 1  and Q 2  and the drive circuit  5  are quite similar to those of the signal transmission apparatus  1 . Therefore, when the transistor Q 2  is placed into an on state while the transistor Q 1  is placed into an off state, current flows from the circuit section  9  through the winding  4   p  of the rotary transformer  4 A to the transistor Q 2 . However, when the transistor Q 1  is placed into an on state while the transistor Q 2  is placed into an off state, current flows from the circuit section  10  through the winding  4   p  of the rotary transformer  4 A to the transistor Q 1 . Accordingly, the direction of current flowing through the winding  4   p  is reversed between the two cases. 
     For example, the following configurations may be applied as a configuration of a passive element circuit  8 A provided at the input stage of the rotary transformer  4 A. 
     (V) A configuration wherein a circuit including an inductance element L 3  and a resistor R 4  connected in series is used; 
     (VI) Another configuration wherein a circuit including an inductance element L 3  and a resistor R 4  connected in series and another resistor R 3  connected in parallel to the series circuit are used; 
     (VII) A further configuration wherein only a resistor R 3  is used and the sum of the inductance of the inductor LL 1  and the inductance of the inductor LL 2  is set lower than that of the conventional signal transmission apparatus; 
     (VIII) A still further configuration wherein the sum of the inductance of the inductor LL 1  and the inductance of the inductor LL 2  in the configuration (V) is set lower than that of the conventional signal transmission apparatus; and 
     (IX) A yet further configuration wherein the sum of the inductance of the inductor LL 1  and the inductance of the inductor LL 2  in the configuration (VI) is set lower than that of the conventional signal transmission apparatus. 
     It is to be noted that FIG. 8 shows the configurations (V) to (IX) described above collectively and therefore shows a configuration same as that of the configuration (VI) or (IX). 
     First, in the configuration (V), a circuit including an inductance element L 3  and a resistor R 4  connected in series is provided at the input stage (stator side) of the rotary transformer  4 A. This corresponds to the configuration of FIG. 8, which lacks the resistor R 3 . In this instance, if the inductance of the inductance element L 3  is substantially equal to the value of the equivalent inductance L (including the recording head  7  as a load) as viewed from the stator side, then the bandwidth is greatest. However, the inductance of the inductance element L 3  is sometimes set to a lower value for the convenience of design of the frequency characteristic. It is to be noted that, although the signal transmission apparatus  1 A in FIG. 8 includes the single series circuit of the inductance element L 3  and the resistor R 4 , if necessary, it can be formed in various modified forms such as, for example, a form wherein a plurality of such series circuits are connected in parallel. 
     In the configuration (VI), a resistor R 3  is connected in parallel to a series circuit of an inductance element L 3  and a resistor R 4 . Accordingly, the configuration (VI) is effective where it is desired to adjust the peak of the frequency characteristic in the configuration (V). 
     In the configuration (VII), only a resistor R 3  is provided in addition to the inductors LL 1  and LL 2  and the resistors RR 1  and RR 2 . Accordingly, the bandwidth can be increased when compared with the configuration (V). However, since the transmission efficiency to the head is deteriorated, the inductance values of the inductors LL 1  and LL 2  must be determined taking the allowance value for the loss of the equivalent inductance L into consideration. Therefore, preferably the sum value of the inductance values of the inductors LL 1  and LL 2  is set lower than that of the conventional signal transmission apparatus. 
     The configuration (VIII) basically has the same configuration as that of the configuration (V). However, since the sum value of the inductance values of the inductors LL 1  and LL 2  is similar to that of the configuration (VII), the configuration (VIII) has effects of the other configurations. 
     The configuration (IX) basically has the same configuration as that of the configuration (VI). However, since the sum value of the inductance values of the inductors LL 1  and LL 2  is similar to that of the configuration (VII), the configuration (IX) has effects of the other configurations. 
     Anyway, since the bandwidth is expanded to the high frequency side as a result of improvement in impedance matching between the rotary transformer and the recording side circuit (drive circuit), also higher frequency components than those in the conventional signal transmission apparatus can be transmitted. 
     It is to be noted that, although also configurations wherein an inductance element is disposed in parallel to the resistor R 3  in the configuration (V) or (VI) are possible, this is equivalent to alteration of the inductance relating to the inductors LL 1  and LL 2 . 
     FIG. 9 illustrates an example of the output characteristic relating to the configuration (VI) in comparison with that of the conventional signal transmission apparatus. The axis of abscissa indicates the frequency (unit: MHz) and the axis of ordinate indicates the magnitude level (unit: dB). 
     In FIG. 9, a curve G 2  indicated by a solid line indicates a characteristic of the circuit according to the present invention, and a curve g 2  indicated by an alternate long and two short dashes line indicates a characteristic of the conventional circuit (the configuration of FIG. 8 in which only the resistor R 3  is provided). From comparison between the curves G 2  and g 2 , it can be seen that the characteristic indicated by the curve G 2  extends to the higher frequency side. 
     While preferred embodiments of the present invention have been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.