Linfinity Microelectronics

Dean Wallace

Chan Shufan

Novel methods and apparatuses for terminating busses are disclosed based upon the number of devices secured to the bus. The impedance of the bus lines varies with the number of devices coupled to the bus. The number of devices coupled to the bus line is determined and a precision resistor is selected based upon the number of devices coupled to the bus matching the expected impedance of the bus. A voltage is generated across the precision resistor with a known current and that voltage is compared with the voltage generated across a controllable resistances such as a FET biased in the linear mode with a like current passing through the fed. A feedback network provides a control voltage to the control electrode of the FET to control the resistance of the FET so that the resistance of the FET equals the selected precision resistance. The same control voltage is coupled to the control electrode of other controllable resistances such as FETs operating in the linear region with each FET terminating a separate signal line. Hence, each FET has a resistance about equal to the resistance of each of the signal lines at the predetermined impedance.

High speed digital bus termination

A controllable active terminator for a computer bus providing low power, small size, switchable termination of a computer bus having a plurality of conductors. The active terminator includes a voltage reference circuit, an enable circuit, a buffer amplifier, and a plurality of output cells. The voltage reference circuit includes a power down circuit which turns the voltage reference circuit off, using the same control signal which also disconnects the termination resistors and output transistors of the output cells. The terminator uses FET technology to produce a low-power, small size, controllable terminator having stable and reliable operating characteristics. The amplifiers used in the active terminator comprise CMOS devices and thus are relatively small and consume relatively low power. When enabled, the voltage reference circuit is used to establish a reference voltage for the linear operation of the output transistors in the output cell. The output current is supplied by terminator power. Consequently, a more reliable and stable bus termination is provided by the present active terminator which uses relatively small and low power components. The output supply current capacity of the present terminator is greater than that provided by the prior art bus terminators.

Controllable actice terminator for a computer bus

A voltage regulator for use in controllable bus terminators providing a source and a sink to a regulated output without clamping circuitry is disclosed. The regulator maintains a voltage at a node by sourcing current into the node when a cable line sinks current from the node and sinking current from the node when a cable line sources current into the node. By avoiding the use of clamping circuitry, a voltage deadband between the regulator output voltage and the clamp circuit voltage is avoided.

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Trabuco Canyon, CA, United States of America

Dean Wallace