Integrated ultra low leakage high voltage protection circuit

• US 5,357,393 A
• Filed: 05/05/1992
• Issued: 10/18/1994
• Est. Priority Date: 05/05/1992
• Status: Expired due to Fees

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Lao, Guillermo, Mojaradi, Mohamad M., Sumida, Dale
• Primary Examiner(s): Hoff, Marc S.
• Assistant Examiner(s): JACKSON, STEPHEN W
• Application Number:
  US07/878,581
• Time in Patent Office: 896 Days
• Field of Search: 257/19, 257/20, 257/21, 361/90, 361/91, 361/117, 361/118, 361/56, 361/58
• US Class Current: 361/56
• CPC Class Codes: H01L 27/0251 for MOS devices

Abstract

An integrated high voltage device with an ultra low leakage input protection circuit to be used in highly sensitive circuits which require ultra low input leakage current. The protection circuit has a common substrate with the integrated circuit device and the common substrate is floating. The floating substrate provides a way of designing a protection circuit with small diodes which have ultra low input D.C. leakage. The protection circuit includes a resistor and two small Zener diodes which can clamp and protect the device during normal operating conditions up to voltages such as 1700 volts.

Claims

1. A high voltage integrated circuit comprising:

a device;

said device having an input and a given node;

a protection means;

said protection means having a common substrate with said device;

said common substrate is floating;

a common input for said protection means and said device;

said protection means having an output;

said protection means having a resistor, a first Zener diode and a second Zener diode;

each of said Zener diodes having a cathode and an anode;

said cathodes of said first and said second Zener diodes being electrically connected to each other through said resistor;

said cathode of said first Zener diode being electrically connected to said common input and said cathode of said second Zener diode being electrically connected to said output of said protection means;

said input of said device being electrically connected to said output of said protection means;

said common input being electrically connected to said device through said output of said protection means;

said floating substrate being electrically connected to said given node of said device whereby the voltage applied to said input is followed by said given node of said device and said substrate; and

said anodes of said first and said second Zener diodes both being electrically connected to said given node of said device for limiting the voltage at said input of said device to a voltage not exceeding the breakdown voltage of said first and said second Zener diodes.

2. The circuit as recited in claim 1, wherein said first diode has a series resistance ranging between 0 ohm to 30 ohm and said second diode have a series resistance ranging between 30 ohm to 150 ohm.

3. The circuit as recited in claim 2, wherein said breakdown voltage is in the range between 18 volts to 25 volts.

4. The circuit as recited in claim 2, wherein an input voltage applied to said input of said protection circuit is between 0 volts to -1700 volts.

5. The circuit as recited in claim 2, wherein an input voltage applied to said input of said protection circuit is between 0 volts to at least -1700 volts.

6. A high voltage integrated circuit comprising:

a device;

said device having an input and a given node;

a protection means;

said protection means having a common substrate with said device;

said common substrate is floating;

a common input for said protection means and said device;

said protection means having an output;

said protection means having a resistor, a first Zener diode and a second Zener diode;

each of said Zener diodes having a cathode and an anode;

said anodes of said first and said second Zener diodes being electrically connected to each other through said resistor;

said anode of said first Zener diode being electrically connected to said common input and said anode of said second Zener diode being electrically connected to said output of said protection means;

said input of said device being electrically connected to said output of said protection means;

said common input being electrically connected to said device through said output of said protection means;

said floating substrate being electrically connected to said given node of said device whereby the voltage applied to said input is followed by said given node of said device and said substrate; and

said cathode of said first and said second Zener diodes being electrically connected to said floating substrate for limiting the voltage at said input of said device to a voltage not exceeding the breakdown voltage of said first and said second Zener diodes.

7. The circuit as recited in claim 6, wherein said first diode has a series resistance ranging between 0 ohm to 30 ohm and said second diode have a series resistance ranging between 30 ohm to 150 ohm.

8. The circuit as recited in claim 7, wherein said breakdown voltage is in the range between 18 volts to 25 volts.

9. The circuit as recited in claim 7, wherein an input voltage applied to said input of said protection circuit is between 0 volts to 1700 volts.

10. The circuit as recited in claim 7, wherein an input voltage applied to said input of said protection circuit is between 0 volts to at least 1700 volts.