Miscellaneous active electrical nonlinear devices – circuits – and – Gating – Signal transmission integrity or spurious noise override
Reexamination Certificate
1998-10-26
2001-04-10
Lam, Tuan T. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Gating
Signal transmission integrity or spurious noise override
C327S310000, C327S311000
Reexamination Certificate
active
06215347
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an undershoot/overshoot protecting circuit, in particular, to an undershoot/overshoot a protecting circuit for removing a noise of a waveform inputting circuit.
2. Description of the Related Art
Generally, crosstalk takes place due to stray coupling of adjacent signals. The crosstalk results in noise of a waveform. The amount of noise varies depending on the level of the waveform and the amount of overshoot or undershoot. Thus, to suppress noise caused by crosstalk, overshoot and/or undershoot should be prevented.
In a waveform inputting circuit for use with an LSI (Large Scale Integrated circuit), to prevent overshoot and/or undershoot from taking place, a clamp diode has been used.
However, in the conventional circuit using such a clamp diode, the through rate of the input waveform cannot be adjusted. Thus, when a waveform with a sharp leading/trailing edge is input, crosstalk takes place between leads of the LSI.
As described in Japanese Patent Laid-open Publication No. Hei6-35582, ringing tends to take place in a high speed bus. So far, the drawback of the above related art has not been solved.
SUMMARY OF THE INVENTION
The present invention is made from the above-described point of view. An object of the present invention is to provide an undershoot/overshoot protecting circuit that adjusts the through rate of an input waveform and prevents crosstalk from taking place between leads of an LSI against a waveform having a sharp leading/trailing edge without an increase of delay time.
A first aspect of the present invention is an undershoot protecting circuit, comprising an inverter circuit for inverting an output signal, a differentiating circuit for differentiating the output signal of the inverter circuit, an undershoot suppressing device for suppressing undershoot of the output signal, and a switching circuit for changing the connecting state of an output signal line so that only when the differentiated output signal of the differentiating circuit exceeds a predetermined threshold level, the output signal is sent through the undershoot suppressing device.
A second aspect of the present invention is an overshoot protecting circuit, comprising a buffering circuit for buffering an output signal, a differentiating circuit for differentiating an output of the buffering circuit, an overshoot suppressing device for suppressing overshoot of the output signal, and a switching circuit for selecting a connecting state of an output signal line so that only when the signal level of the differentiated output signal exceeds a predetermined threshold value, the output signal is sent through the overshoot suppressing device.
The undershoot/overshoot protecting circuit according to the present invention prevents undershoot and/or overshoot from taking place. In addition, the time period until the signal level of the waveform becomes a predetermined threshold level does not vary. Thus, the undershoot/overshoot protecting circuit can suppress crosstalk noise from taking place without an increase of delay time.
These and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of a best mode embodiment thereof, as illustrated in the accompanying drawings.
REFERENCES:
patent: 4532475 (1985-07-01), Ishigaki et al.
patent: 5952736 (1999-09-01), Matsubara
patent: 57-203122 (1982-12-01), None
patent: 6-35582 (1994-02-01), None
patent: 7-334281 (1995-12-01), None
Lam Tuan T.
NEC Corporation
Nguyen Hiep
Sughrue Mion Zinn Macpeak & Seas, PLLC
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