Fairchild Semiconductor Corporation

Trenor F Goodell

Myron J Miske

Oscar W Freitas

James B Boomer

Jennifer Richards

A bus switch for transferring logic signals between nodes without the problems associated with overvoltage conduction. The bus switch is an FET switch including a single primary transfer transistor. The bulk of the transfer transistor is coupled to an arbitration circuit that establishes a pseudo high-potential power rail. The pseudo high-potential rail is the highest of a potential associated with the first node, the second node, and a standard high-potential supply rail. The arbitration circuit includes regulating diode devices in parallel, one of which passes to the pseudo high-potential rail the potential associated with the first node and the other the potential associated with the second node, whichever is higher. If both are substantial equal to the potential of the standard high-potential rail, that potential is passed to the pseudo high-potential rail.

FET switch with overvoltage protection

A translation switch is described with a transfer MOS transistor that connects a first node to second node where the first node is referenced to a higher voltage than is the second. A pseudo-rail generator drives the gate of the MOS transistor and provides a p-rail reference voltage lower in voltage to that of the first node. The generator includes a selectively enabled active clamping circuit that clamps the gate of the MOS transfer transistor to the p-rail potential and sinks current from the p-rail when higher voltages appear on the p-rail to thereby maintain the p-rail at a substantially constant potential.

Translating switch circuit with disabling option

A high-frequency switch circuit having an MOS pass gate or transfer transistor. The switch circuit of the invention includes a first impedance element coupled to the gate of the transfer transistor and, preferably, an alternative second impedance element coupled to the bulk of the transfer transistor. One or both of the impedance elements substantially negates the low-parasitic shunt capacitance associated with the transfer transistor that controls signal attenuation under high frequency operation. The impedance element is coupled in series with that parasitic capacitance to increase substantially the impedance of that pathway, thereby increasing substantially the passable bandwidth. The impedance element may simply be a resistor. The switch circuit is suitable for use in an array of applications, including signal propagation in computing systems, routers, and flat panel screen displays.

High frequency MOSFET switch

A wave shaping circuit for shaping the transition edges of switching electrical signals. The wave shaping circuit controls voltage output as a function of time and is applicable in digital and analog systems. The shaping circuit includes one or more stages having the capability to conduct current simultaneous during signal transitions. Each simultaneous conduction current stage is coupled to a current mirror circuit powered by a power supply rail. The current mirror circuit is coupled to a capacitive element that is charged or discharged by current provided through the simultaneous conduction current stage or stages. Through selectable design of the simultaneous conduction stages, the current mirror circuit, and the capacitive element, the designer can tailor the shape of the transition curve as the input signal is propagated through the shaping circuit to the output.

Wave shaping circuit

A bus switch for transferring logic signals between nodes without the problems associated with undershoot conduction. The bus switch is an FET switch including a single primary transfer transistor. The bulk of the transfer transistor is coupled to a differential logic sense circuit that is designed to establish a pseudo low-potential power rail. The logic sense circuit is coupled to the two transfer nodes and a standard low-potential power rail. It compares the potentials associated with the transfer node signals and the low-potential rail and selects the one with the lowest potential to establish the potential of the pseudo low-potential rail. The logic sense circuit provides for active selection of the lowest potential element, including under very small undershoot conditions. The logic sense circuit may be established in a variety of ways, preferably by including a differential comparator pair, one of associated with one of the two transfer nodes and the other differential comparator associated with the other transfer node. Outputs of the differential pair control logic drivers that in turn regulate the transfer node, or standard low-potential rail to be coupled to the pseudo low-potential power rail. This arrangement ensures that there will be no parasitic conduction of the transfer transistor during undershoot conditions.

Active undershoot hardened fet switch

A logic level converter for translating CMOS logic signals to into differential logic signal pairs such as those associated with ECL levels. The converter includes a first converter branch coupled to the switchable CMOS level input and it provides a first switchable translated output. A second converter branch is not coupled to the input nor is it coupled to the first converter branch. The second converter branch provides a fixed reference signal output around which the output of the first converter branch switches. Changes in the input signal to the first converter branch cause its output potential to be more than or less than the potential of the fixed reference signal supplied by the second converter branch. The components of the respective branches may be tailored to position the fixed signal at a selectable level and to define the differential between the two output signals. The current associated with the converter is mirrored through both branches to minimize the effects of fabrication, temperature, and/or power supply vagaries.

High speed low skew CMOS to ECL converter

A multiplexer for selecting a single output signal from a plurality of input signals. For a plurality of complementary input signal pairs in particular, the multiplexer includes for each pair of complementary input signals a control sub-circuit having a selection switch and a common resistance in parallel. The switch and the common resistance have a common low-potential node that is tied to a pair of resistances that are in parallel, wherein each of the parallel resistances is coupled to the respective high-potential nodes of a differential amplifier. A particular pair of incoming complementary input signal pairs controls the differential amplifier. An off-circuit selection signal selects which switch of a plurality of control sub-circuits is activated. When a switch is on, it creates a bypassing of the common resistance, thereby enabling the turn-on of output drivers coupled to the differential amplifier. When a switch is off, the potential drops across the common resistance and the parallel resistances reduce the potential at the output drivers' control nodes enough to block their turn-on. As a result, the only output drivers providing signal output are those associated with the one selected control sub-circuit having its switch turned on.

Low voltage, high speed multiplexer

A bus switch for transferring logic signals between nodes without the problems associated with undershoot conduction. The bus switch is an FET switch including a single primary transfer transistor. The bulk of the transfer transistor is coupled to a bulk regulating circuit including a pseudo low-potential power rail. The pseudo low-potential rail is coupled to one arbiter circuit associated with one of the two circuit transfer nodes and a second arbiter circuit associated with the other of the two transfer nodes. The arbiter circuits are coupled to their respective nodes or pads and to a common low-potential supply rail. The arbiter selects for coupling to the pseudo low-potential rail the signal of the lower potential between that at the pad and that of the low-potential rail. This arrangement ensures that there will be no parasitic conduction of the transfer transistor during undershoot conditions. In an alternative embodiment that may be used to minimize the vagaries associated with process variations, the transfer transistor's gate may be independently coupled to a second pseudo low-potential power rail.

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Peaks Island, ME, United States of America

Trenor F Goodell