Optimized active SCSI termination technique
AssigneeMicro Linear Corporation
InventorsDaniel D. Culmer, Mark R. Vitunic
Life of this patent
Estimating the term…
Abstract
The invention employs an active element, a p-channel MOSFET, between a regulated voltage and a SCSI terminating line. An "ideal" current source terminator is most effective when a signal line is negated (low-to-high transition), whereas a resistive terminator is most effective when a signal line is asserted (high-to-low transition). The I-V characteristics of a p-channel MOSFET, wherein the relationship between the termination voltage and the termination current is characterized by a nonlinear and smooth voltage versus current curve, provide an optimized transient response for signal negations and signal assertions on a SCSI bus.
Claims8
An active SCSI termination circuit comprising:
- a. a first means for terminating a signal line on a SCSI bus, comprising a first p-channel MOSFET, having a source, a gate, a drain, and an aspect ratio approximately twenty-four times larger than an aspect ratio of a reference MOSFET having a gate, a source and a drain and the drain of the p-channel MOSFET coupled to the signal line;
- b. a second means for terminating the signal line, comprising a second p-channel MOSFET, having a source, a gate, a drain, and an aspect ratio approximately equal to the aspect ratio of the reference MOSFET and the drain of the second p-channel MOSFET coupled to the signal line;
- and
- c. means for selecting between the first p-channel MOSFET and the second p-channel MOSFET.
An active SCSI termination circuit comprising:
- a. a first means for terminating a plurality of signal lines on a SCSI bus, comprising a first plurality of p-channel MOSFETs, each p-channel MOSFET of the first plurality having a source, a gate, a drain, and an aspect ratio approximately twenty-four times larger than an aspect ratio of a reference MOSFET having a gate, a source and a drain and the drain of each p-channel MOSFET of the first plurality coupled to one of the plurality of signal lines;
- b. a second means for terminating the plurality of signal lines, comprising a second plurality of p-channel MOSFETs, each p-channel MOSFET of the second plurality having a source, a gate, a drain, and an aspect ratio approximately equal to the aspect ratio of the reference MOSFET and the drain of each p-channel MOSFET of the second plurality coupled to one of the plurality of signal lines;
- and
- c. means for selecting between the first plurality of p-channel MOSFETs and the second plurality of p-channel MOSFETs.
An active SCSI termination circuit coupled with means for receiving a signal from a peripheral device via a signal line, the termination circuit with means for passing a maximum termination current and dropping a minimum termination voltage when the signal line is asserted and the termination circuit with means for pulling the signal line to a maximum termination voltage and passing a minimum termination current when the signal line is negated;
- wherein the relationship between the termination voltage and the termination current is characterized by a nonlinear and smooth voltage versus current curve plotted in the first quadrant of a Cartesian coordinate system and having a negative slope varying continuously from a first point having a first slope to a second point having a second slope wherein the coordinates of the first point comprise the maximum termination voltage and the minimum termination current and wherein the coordinates of the second point comprise the minimum termination voltage and the maximum termination current, such that the negative slope becomes increasingly and continuously more negative as the termination voltage increases from the first point to the second point.
Dependencies are inferred from the claim text.