Texas Instruments Corporation

Dale P Stein

Steven E Marum

James Craig Spurlin

Sam M Weaver

Jose M Soltero

A hold circuit for holding a digital switch, having an input and an output, at the level of the last driven state substantially independently of the output impedance of a circuit driving the digital switch. The hold circuit includes an inverter having an input connected to the output of the digital switch and having an output, and a variable resistor having a port connected to the output of the inverter and having a port connected to the input of the digital switch. In a preferred embodiment, a bus-hold integrated circuit servicing Insulated Gate FET digital switches can be operated from either of two distinct ranges of supply voltage (V ). The magnitudes of the holding currents for the higher range of V are nearly the same as those for the lower range of V . This characteristic is achieved by changing the resistance in the feedback path of the bus-hold circuit according to the applied V . Resistance is increased by turning off wider channel IGFETs that are connected in parallel with narrower channel IGFETs when the higher range of V is applied. When the lower range of V is applied the wider channel IGFETs are switched on and the resistance of the holding current path is decreased in proportion to the decrease in V .

Vcc-compensated bus-hold circuit

A transistor (14) having a plurality of sub-transistors (26a-f) includes a voltage controlling device (45). The voltage controlling device induces a current through an elongated gate (24) producing a voltage drop across the elongated gate (24) by providing a path between one end of the gate and ground (32). The voltage drop across the elongated gate (24) sequentially reduces the gate voltage present at each of the sub-transistors (29a-f), thereby reducing the amount of current which the sub-transistors (29a-f) can conduct. The voltage controlling circuit (45) gradually reduces the current through the elongated gate (24), thereby increasing the amount of current through the sub-transistors (29a-f). The time interval over which the conductive device induces a current through the elongated gate (24) can be adjusted by positioning the connection to the gate of a transistor (62) along the elongated gate (24). The limiting of current through the output sub-transistors (29a-f) for a predetermined time interval reduces the generation of output noise by controlling the rate at which current is changing in that output.

Integrated circuit to reduce switching noise

A transistor (14) having a plurality of sub-transistors (29a-f) includes a voltage controlling device (45). The voltage controlling device induces a current through an elongated gate (24) producing a voltage drop across the elongated gate (24) by providing a path between one end of the gate and ground (32). The voltage drop across the elongated gate (24) sequentially reduces the gate voltage present at each of the sub-transistors (29a-f), thereby reducing the amount of current which the sub-transistors (29a-f) can conduct. The voltage controlling circuit (45) gradually reduces the current through the elongated gate (24), thereby increasing the amount of current through the sub-transistors (29a-f). The time interval over which the conductive device induces a current through the elongated gate (24) can be adjusted by positioning the connection to the gate of a transistor (62) along the elongated gate (24). The limiting of current through the output sub-transistors (29a-f) for a predetermined time interval reduces the generation of output noise by controlling the rate at which current is changing in that output.

A complimentary output pair (10) having a P-channel transistor (12) and an N-channel transistor (14) prevents output voltage spikes due to rapid changes in current with respect to time at the V.sub.cc power supply and ground (32) nodes by using a 'graded turn-on.' Both the P-channel transistor (12) and the N-channel (14) utilize a serpentine polysilicon gate (16), (24), in order to sequentially turn on the sub-transistors in response to a changing input. Pull-up (36) and pull-down (40) transistors are used to turn the sub-transistors (21a-j, 29a-f) off simultaneously.

Growing community of inventors

Sherman, TX, United States of America

Dale P Stein