Wave transmission lines and networks – Plural channel systems – Having branched circuits
Reexamination Certificate
1999-08-11
2001-11-20
Bettendorf, Justin P. (Department: 2817)
Wave transmission lines and networks
Plural channel systems
Having branched circuits
C333S02400C, C333S020000
Reexamination Certificate
active
06320475
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a printed circuit board and an electronic device for connections between circuits in a personal computer and office automation devices.
This application is based on Japanese Patent Application No. 10-229138, the contents of which are incorporated herein by reference.
2. Background Art Including Information Disclosed Under37 CFR 1.97 and 1.98
In general, office automation devices such as personal computers and workstations include a number of printed circuit boards. As demand for acceleration of data processing and reduction in size has recently increased, the clock frequencies in the circuits have increased to more than several 100 MHz.
As the clock frequencies increased, however, unnecessary radiant noise may occur in the circuits on the printed circuit board. Because of the increase of the clock frequencies, the differences in length between connection lines may change the inductance. As the result, input signals show waveforms which include ringing, as shown in
FIG. 3
(with the overshoot to 9V and the undershoot to −7V), which leads to the occurrence of unnecessary radiant noise. Further, when the terminating resistances change due to the irregularity of manufactured transmission lines, the characteristics of the impedance may be unbalanced, ringing may occur in the waveforms, and reflection of signals may occur, causing a malfunction or destruction of the semiconductor device.
Japanese Unexamined Patent Application, First Publication No. Hei 4-97562 discloses a technique for adjusting terminating resistances to suppress ringing in waveforms by selecting one of a number of terminating resistances. Japanese Unexamined Patent Application, First Publication No. Hei 6-152355 discloses a technique to suppress the ringing by a dummy line whose one end is open or connected to the ground. Japanese Unexamined Patent Application, First Publication No. Hei 6-177612 discloses a technique to manufacture a printed circuit board of a material which can suppress the ringing.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a printed circuit board and an electronic device which suppress ringing and securely prevents the malfunction and destruction of the device.
The printed circuit board of the present invention comprises: a main transmission line; and additional transmission lines positioned on both sides of the main transmission line and parallel-connected to the main transmission line by way of selectors.
The selectors may be semiconductor switches. A plurality of pairs of an additional transmission line and a selector may be provided.
The printed circuit board comprises: a first transmission line; second and third transmission lines positioned on both sides of the first transmission line and parallel-connected to the first transmission line; and first to fourth selectors, each selector having first and second terminals, the each selector being able to connect and disconnect the first terminal to the second terminal. One end of the first transmission line is connected to the first terminal of the first selector and to the first terminal of the second selector. The second terminal of the first selector is connected to one end of the second transmission line. The second terminal of the second selector is connected to one end of the third transmission line. The other end of the second transmission line is connected to the first terminal of the third selector. The other end of the third transmission line is connected to the first terminal of the fourth selector. The other end of the first transmission line is connected to the second terminal of the third selector and to the second terminal of the fourth selector.
REFERENCES:
patent: 5136265 (1992-08-01), Pritchett
patent: 5424696 (1995-06-01), Nakahara et al.
patent: 1-112061 (1989-07-01), None
patent: 2-23002 (1990-06-01), None
patent: 4-97562 (1992-03-01), None
patent: 6-152355 (1994-05-01), None
patent: 6-177612 (1994-06-01), None
Bettendorf Justin P.
Jones Stephen E.
NEC Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
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