National Semiconductor Corporation

Sam S Ochi

James B Compton

Adib R Hamade

Daniel D Culmer

Ronald W Russell

JFET and bipolar transistor devices are combined into an analog signal switching circuit. A JFET acts as a switch device for controlling analog signals. The JFET gate is charged through a bipolar transistor to turn if off and discharged through a second bipolar transistor to turn it on. A second JFET is used to control the conduction of the second bipolar transistor so that it only conducts heavily when a high slew rate is needed. The circuit can switch analog signals very rapidly and yet has very low quiescent current drain in both off and on states. The circuit is very simple and is amenable to monolithic integrated circuit construction.

JFET switch circuit

A base junction transistor inverter circuit will be driven into the saturation region if the drive current is large enough. In such circumstances, the collector voltage can go below the base voltage and approaches the emitter voltage. A circuit is provided to keep the transistor out of saturation and is comprised of a p-channel field effect transistor (JFET) connected between the base and collector of the junction transistor. The JFET is connected such that when the drive current increases and the junction transistor approaches saturation, the drive current is diverted through the JFET and into the substrate. The same clamp can be implemented by using a pnp junction transistor in combination with an n-channel JFET.

JFET base junction transistor clamp

A JFET is coupled in parallel with a bipolar transistor to produce a composite structure that has improved signal transfer characteristics in certain circuit applications. While useful with discrete devices, the combination is readily achieved in integrated circuit form.

Composite JFET-bipolar transistor structure

JFET and bipolar transistor devices are combined into an analog signal switching circuit. A JFET acts as a switch device for controlling analog signals. The JFET gate is charged through a bipolar transistor to turn it off and discharged through a second bipolar transistor to turn it on. A second JFET is used to control the conduction of the second bipolar transistor so that it only conducts heavily when a high slew rate is needed. The circuit can switch analog signals very rapidly and yet has very low quiescent current drain in both off and on states. The circuit is very simple and is amenable to monolithic integrated circuit construction.

JFET switch circuit and structure

A pair of FET's are coupled in series between the emitter and collector of a bipolar transistor and the juncture of the FET's coupled to the bipolar transistor base. The FET gates are coupled to the bipolar transistor collector. When a current is passed through the emitter-collector terminals in excess of a threshold value, a constant voltage will appear over a substantial current range. The constant voltage is related to FET Vp and can be used to compensate or track integrated circuits that contain both FET's and bipolar transistors.

Circuit combining bipolar transistor and JFET's to produce a constant

A field effect transistor (FET) is designed to act as an off-on type switch by the control of a driver voltage applied to its gate electrode. A driver circuit, responsive to a toggling current, provides a control of gate electrode voltage. The circuit includes means for rapidly switching the FET on and off while drawing relatively low current in the off and on states. Improvements relate to means for speeding up turn on time and reducing charge transferred to the circuit being switched by the FET.

Field effect transistor switch

A differential input is applied to four bridge-connected field effect transistors. The bridge drives a differential common base transistor stage. The output can be either differential or single ended as desired taken from the transistor collectors. The circuit provides good common mode rejection and good differential response to signals over a common mode range that exceeds the voltage of the power supply.

Wide common mode range differential amplifier

A circuit for cancelling the offset voltage of a signal amplifier includes a second amplifier and a third amplifier connected to the outputs of the signal amplifier and the second amplifier. A capacitor is connected between the inputs of the second amplifier for storing the offset voltages of the amplifiers thereon. A switch connects the output of the third amplifier to the capacitor and a switch connects the inputs of the signal amplifier together during offset correction. When the offset voltages are stored on the capacitor, the switches open to permit signal amplification and cancellation of the offset voltages. In a second embodiment, a second capacitor stores the instantaneous amplitude of the signal being amplified and supplies it to an input of the second amplifier such that a discontinuity will not appear in the circuit output during offset correction.

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San Jose, CA, United States of America

Sam S Ochi