Active solid-state devices (e.g. – transistors – solid-state diode – Regenerative type switching device – Device protection
Reexamination Certificate
1999-07-08
2001-02-13
Hardy, David (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Regenerative type switching device
Device protection
C257S146000, C257S357000
Reexamination Certificate
active
06188088
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of electrostatic protection of electronic devices.
2. Prior Art
Field effect devices, now more generally referred to as MOS devices, are characterized by an insulated gate over a channel region extending between doped source and drain regions. The gate insulation is a relatively thin oxide layer which, together with the relatively small gate, forms a capacitor of low capacitance and low breakdown voltage, usually approximately on the order of 10 volts. However, a typical electrostatic discharge as may occur when handling the device or associated circuitry in dry weather may easily reach 1,000 volts or more. Without electrostatic discharge protection, gate oxides will break down in a destructive manner when subjected to such high voltages, even from a relatively high impedance source, rendering the circuit permanently inoperative. As a result, various circuit designs and techniques have been used in the prior art to provide protection of MOS type integrated circuits, with various standardized testing procedures being used to verify satisfactory electrostatic discharge survival. By way of example, the IEC 1000-4-2 model requires electrostatic discharge protection for voltage spikes up to 15,000 volts, the voltage spike being delivered through a resistor of a predetermined value.
BRIEF SUMMARY OF THE INVENTION
Electrostatic discharge protection for analog switches using silicon-controlled rectifiers is disclosed. Two silicon-controlled rectifiers (SCRs) may be formed in a common isolation region of an integrated circuit. Each SCR has its gate and cathode coupled together so as to be self triggering. The SCRs are connected in parallel in reverse polarity and coupled between the analog switch input or output and ground. In normal switch operation, both SCRs will be off, though when the voltage of the protected switch connection exceed on of the supply rails, one of the SCRs will trigger, providing a low impedance connection to ground. Once the voltage returns to normal, the SCR will automatically release.
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Blakely , Sokoloff, Taylor & Zafman LLP
Hardy David
Maxim Integrated Products Inc.
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