US 3,947,727 AGranted

Protection circuit for insulated-gate field-effect transistors

AssigneeRCA Corporation

InventorRoger Green Stewart

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Abstract

Two current-carrying paths are connected in parallel between a signal input terminal and an internal node to which are connected the gate electrodes of insulated-gate field-effect transistors to be protected. One path includes the conduction path of a first transistor of one conductivity type connected in series with a first diode poled in a direction to charge the internal node and the other path includes the conduction path of a second transistor of second conductivity type in series with a second diode poled in a direction to discharge the internal node. The control electrodes of the first and second transistors are connected to points of operating potential rendering the first transistor conductive in the source follower mode for input signals of one polarity and rendering the second transistor conductive in the source follower mode for input signals of opposite polarity.

Claims13

Dependent claims

A protection circuit for an insulated gate field transistor (IGFET) whose gate is connected to an input node, said protection circuit comprising:

first and second asymmetrical devices each having a low impedance forward current direction and a high impedance reverse current direction;
first and second transistors of first and second conductivity types, respectively, each having a conduction path and a control electrode;
a signal input terminal;
means connecting said first asymmetrical conducting device in series with the conduction path of said first transistor between said signal input terminal and said input node, with said first asymmetrical conducting device connected to conduct current from said signal input terminal to said input node in its low impedance direction;
means connecting said second asymmetrical conducting device in series with the conduction path of said second transistor between said signal input path and said input node, with said second asymmetrical conducting device connected to conduct current from said input node to said input terminal in its low impedance direction;
and
means for connecting the control electrodes of said first and second transistors to first and second different bias points, respectively.

4 more elements

The combination of:

first and second terminals for the application therebetween of an operating potential;
an input node;
an output node;
and a signal input terminal;
first and second insulated-gate field-effect transistors (IGFETs) of first and second conductivity type, respectively, each IGFET having a drain and a source defining the ends of a conduction path, and a gate;
means connecting the gates of said first and second IGFETs in common to said input node;
means connecting the drains of said first and second IGFETs in common to said output node;
means connecting the source of said first IGFET to said first terminal;
and means connecting the source of said second IGFET to said second terminal;
and
a protection circuit comprising:
first and second diodes;
third and fourth IGFETs of first and second conductivity type, respectively;
means connecting the conduction path of said third IGFET in series with said first diode between said signal input terminal and said input node;
means connecting the conduction path of said fourth IGFET in series with said second diode between said signal input terminal and said input node;
said second diode being poled in a direction opposite to said first diode;
and
means connecting the gate electrode of said fourth IGFET to said first terminal and means connecting the gate electrode of said third IGFET to said second terminal.

15 more elements

Dependencies are inferred from the claim text.