Compositions – Magnetic – Iron-oxygen compound containing
Reexamination Certificate
2002-07-12
2004-08-10
Koslow, C. Melissa (Department: 1755)
Compositions
Magnetic
Iron-oxygen compound containing
C252S062630, C252S062590
Reexamination Certificate
active
06773619
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic core for a transformer used in a high speed data communication modem in a digital subscriber line (generally called xDSL), such as an asymmetric digital subscriber line (ADSL) and a very high-bit rate digital subscriber line (VDSL), and a composition of the same, particularly relates to a magnetic core for a transformer which exhibits excellent total harmonic distortion (THD) characteristics of a transmission waveform in a broad frequency band and a wide temperature range at the time of data communication and a composition of the same.
2. Description of the Related Art
In recent years, in the field of electronics, equipments have been required to be made smaller in size, smaller in thickness and improved in performance. Furthermore, in the field of communication equipment, the impedance of the primary coil in the pulse transformer for interfacing with the Integrated Services Digital Network (ISDN) etc. has to be increased in a broad frequency band to improve the transmission characteristics. Therefore, the primary coil is required to have a high inductance. The I.430 and other standards of the ITU (International Telecommunication Union)-T required that at least 20 mH be secured for the inductance of the primary coil of the pulse transformer.
Further, to reduce the size and thickness of electronic equipments in this way, the transformer has to be made smaller and thinner. Therefore, the necessary inductance is secured by increasing the magnetic permeability of the material of the magnetic core used for the transformer (Japanese Unexamined Patent Publication (Kokai) No. 6-263447, Japanese Unexamined Patent Publication (Kokai) No. 7-94314, Japanese Unexamined Patent Publication (Kokai) No.7-169612, Japanese Unexamined Patent Publication (Kokai) No. 7-211530, Japanese Unexamined Patent Publication (Kokai) No.7-278764, Japanese Unexamined Patent Publication (Kokai) No. 7-297034, Japanese Unexamined Patent Publication (Kokai) No. 8-85821, Japanese Unexamined Patent Publication (Kokai) No. 8-97045, Japanese Unexamined Patent Publication (Kokai) No.9-246034, Japanese Unexamined Patent Publication (Kokai) No. 10-12447, and Japanese Unexamined Patent Publication (Kokai) No. 10-335130), reducing the thickness of the transformer (Japanese Unexamined Patent Publication (Kokai) No. 7-201582, Japanese Unexamined Patent Publication (Kokai) No. 7-201585, Japanese Unexamined Patent Publication (Kokai) No. 7-201588, Japanese Unexamined Patent Publication (Kokai) No. 7-201589, and Japanese Unexamined Patent Publication (Kokai) No. 7-201590), mirror-polishing the bonding surface in the case of a split-type magnetic core such as an EE shape (Japanese Unexamined Patent Publication (Kokai) No. 9-246034), etc.
Even in a transformer of a modem used for connecting a telephone line transmitting an analog signal and a data terminal or computer handling a digital signal, a high inductance is similarly required (Japanese Unexamined Patent Publication (Kokai) No. 11-176643 and Japanese Unexamined Patent Publication (Kokai) No. 11-186044).
Furthermore, due to the rapid spread of the Internet, a demand has risen for communication systems enabling higher speed communication of large quantities of data compared with the ISDN, etc. New communication systems called the xDSL (x digital subscriber line) have been developed. The ADSL (asymmetric digital subscriber line) and the VDSL (very high-bit rate digital subscriber line) enabling a higher communication speed, etc. are included in the xDSL technique.
The xDSL requires a modem for converting a digital signal to and from an analog signal and the modem requires a transformer for insulating from a line. In the xDSL technology, transmission speed is much higher (16 kb/s to 9 Mb/s in ADSL and 1.5 Mb/s to 52 Mb/s in VDSL) and the operating frequency band is also high (30 kHz to 1.1 MHz in ADSL and 1 MHz to 10 MHz in VDSL). Therefore, the transformer used for a modem may be reduced in the inductance for raising the impedance compared with the conventional transformers for ISDN. Accordingly, the magnetic permeability of the material of the magnetic core of the transformer may be made smaller than that in the past and mirror-polishing of the bonding surfaces is not required even in the case of a split-type magnetic core such as an EE shape.
On the other hand, in high speed data communications using such xDSL, the transformer used in the modem for transmitting a data signal at a high speed has to have a small distortion of the transmission waveform and a small noise and has to be reduced in the rate of occurrence of transmission error, so that a material of the magnetic core having a small THD is sought. Therefore, the loss in the AC magnetic field (the eddy current loss, the hysteresis loss, and the residual loss) has to be reduced.
Note that the THD means the ratio of the total harmonics and the noise component with respect to the basic signal of the input data at the time of data communication as expressed by the following equation (1), so the THD becomes smaller the smaller the distortion of the transmission waveform or the smaller noise.
THD
(dB)=20 log{(harmonics+noise)/(basic wave+harmonics+noise)} (1)
As a material of a magnetic core for reducing the THD, the present inventors have developed an Mn—Zn based ferrite material described in the U.S. patent application Ser. No. 09/944,590 (corresponding to the Japanese Patent Application No. 2000-279101). The Mn—Zn based ferrite material filed as a prior application reduces the THD in a broad frequency band by specifying a range of its main composition, but there is a demand for one capable of reducing the THD in the broad frequency band from the other approach.
Furthermore, the Mn—Zn based ferrite material filed as a prior application reduces the THD in a wide temperature range (−40° C. to +85° C.) but becomes minimum at around −10° C. and the THD worsens to about several dB on the higher temperature side and on the lower temperature side of the temperature showing the minimum value. Thus, it is desired to reduce the THD value in frequently used temperatures of around 25° C.
Note that effects of the main composition and additives in Mn—Zn based ferrite materials are reported in various ways so far but there has been no report on a technique of reducing the THD in a broad frequency band and/or a wide temperature range.
For example, a technique described in the Japanese Unexamined Patent Application No. 4-336401 Publication is only for attaining high magnetic permeability in a high frequency range by limiting a main composition range and adding additives (SiO
2
, CaO, Nb
2
O
5
and Bi
2
O
3
) by suitable amounts. Also, a technique described in the Japanese Unexamined Patent Application No. 10-50512 Publication is only for attaining high magnetic permeability in a high frequency range by limiting a main composition range, adding additives (SiO
2
, CaO, Nb
2
O
5
and Bi
2
O
3
) by suitable amounts, limiting a range of an absolute value of a complex initial permeability in a broad frequency range and limiting a range of a value of DC resistivity. Furthermore, a technique described in the Japanese Unexamined Patent Application No. 6-151151 Publication is only for attaining high magnetic permeability in a high frequency range by limiting a main composition range and adding additives (SiO
2
, CaO, Sb
2
O
2
, Nb
2
O
5
and Ta
2
O
5
) by suitable amounts. Also, a technique described in the Japanese Unexamined Patent Application No. 9-326310 Publication is only for attaining low losses by limiting a main composition range and adding additives (SiO
2
, TiO
2
, CaO, Nb
2
O
5
and Ta
2
O
5
) by suitable amounts.
Note that a technique described in the Japanese Unexamined Patent Application No. 6-290926 Publication specifies a composition difference of ZnO between a surface and inside of a sintered core in low-temperature sintering in order to provide a low-loss magnetic materia
Hirai Ippou
Sezai Yuji
Watanabe Masahiko
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