Electrostatic discharge protection for a transformer balun

Patent metadata

Field	Value
Publication number	US-9806521-B2
Application number	US-201414527205-A
Country	US
Kind code	B2
Filing date	Oct 29, 2014
Priority date	Oct 29, 2014
Publication date	Oct 31, 2017
Grant date	Oct 31, 2017

Abstract

A balun includes an input coil and an output coil with first and second outputs that vary during normal operation. The output coil has a center point connection that remains substantially constant during normal operation. An ESD circuit provides a low impedance path between the center point connection and chip ground when the voltage at the center point connection is above a first threshold voltage or below a second threshold voltage and isolates the center point connection from chip ground otherwise. Another ESD protection circuit provides ESD protection for other input or output terminals of the integrated circuit by selectively coupling the other input or output terminals to chip ground. Thus, a charge that builds up between one of the balun outputs and another terminal on the integrated circuit can be safely dissipated.

First claim

What is claimed is:

1. An apparatus comprising:
an input coil and an output coil having a center point connection, the input coil and the output coil forming a balun; and
an electrostatic discharge (ESD) circuit configured to couple the center point connection to a reference voltage node through the ESD circuit responsive to a voltage at the center point connection being above a first threshold voltage and the ESD circuit is responsive to isolate the center point connection from the reference voltage node responsive to the voltage at the center point connection being below the first threshold voltage and above a second threshold voltage;
wherein ESD circuit is further configured to couple the center point connection to the reference voltage node through a first circuit responsive to the voltage at the center point connection being below the second threshold voltage;
wherein the voltage at the center point connection varies but is substantially stable during normal operation as compared to positive and negative outputs of the balun and the voltage at the center point connection remains within several tenths of volts of zero volts during normal operation.

2. The apparatus as recited in claim 1 wherein the reference voltage node is a ground node.

3. The apparatus as recited in claim 1 wherein the ESD circuit comprises at least first and second diodes in an antiparallel configuration to thereby provide a low impedance path from the center point connection, through one of the first and second diodes, to the reference voltage node in response to the voltage at the center point connection being above the first threshold voltage or the voltage at the center point connection being below the second threshold voltage.

4. The apparatus as recited in claim 1 , wherein the balun is disposed in an integrated circuit.

5. The apparatus as recited in claim 4 further comprising a second electrostatic discharge (ESD) circuit coupled to terminals of the integrated circuit separate from the balun and the second ESD circuit is coupled to the reference voltage node.

6. The apparatus as recited in claim 5 further comprising:
a first and second output pad coupled to the balun;
a third output pad coupled to circuits in the integrated circuit and coupled to the second ESD circuit.

7. The apparatus as recited in claim 1 wherein the input coil and output coil forming the balun are formed separately from an integrated circuit on which the ESD circuit is disposed.

8. A method of providing electrostatic discharge protection for a balun comprising:
supplying a differential signal from an output coil of a balun having a center point connection that fluctuates during normal operation but remains within several tenths of volts of zero volts during normal operation; and
responsive to a voltage of the center point connection of the output coil of the balun going above or below respective first and second threshold voltages, providing a low impedance path to a reference voltage node for the output coil from the center point connection.

9. The method as recited in claim 8 wherein the reference voltage node is ground.

10. The method as recited in claim 8 wherein providing the low impedance path comprises turning on a first portion of a diode circuit when the voltage at the center point connection of the output coil is above the first threshold voltage and turning on a second portion of the diode circuit when the voltage at the center point connection is below the second threshold voltage, to thereby provide the low impedance path to the reference voltage node.

11. The method as recited in claim 10 , wherein the balun is disposed in an integrated circuit.

12. The method as recited in claim 11 further comprising providing a low impedance path to the reference voltage node for one or more input or output terminals on the integrated circuit through an electrostatic discharge (ESD) circuit coupled to the one or more input or output terminals, the ESD circuit being separate from the diode circuit.

13. The method as recited in claim 8 further comprising during normal operation the voltage of the center point connection is substantially stable as compared to first and second outputs of the output coil.

14. An apparatus comprising:
a balun including an input coil and an output coil having a center point connection and a first and second connection of the output coil coupled respectively to first and second output pads; and
a first ESD circuit coupled at a first node of the first ESD circuit to the center point connection and coupled at a second node to a reference voltage node, the first ESD circuit responsive to a voltage at the center point connection being above or below respective first and second threshold voltages to provide a low impedance path from the center point connection to the reference voltage node through the first ESD circuit and when the voltage at the center point connection is below the first threshold voltage and above the second threshold voltage the center point connection is isolated from the reference voltage node by the first ESD circuit;
wherein the voltage at the center point connection varies but is substantially stable during normal operation as compared to positive and negative outputs of the balun and the voltage at the center point connection remains within several tenths of volts of zero volts during normal operation.

15. The apparatus as recited in claim 14 wherein the reference voltage node is ground.

16. The apparatus as recited in claim 14 wherein further comprising a second electrostatic discharge (ESD) circuit coupled to provide a path between an input or output pad and the reference voltage node responsive to an ESD event including the input or output pad.

17. The apparatus as recited in claim 16 wherein the apparatus is an integrated circuit and the balun, the second ESD circuit, and the first ESD circuit are disposed on the integrated circuit.

18. The apparatus as recited in claim 16 wherein the first ESD circuit and the second ESD circuit are disposed on an integrated circuit and the balun is disposed on a separate substrate, electrically and mechanically coupled to the integrated circuit.

19. The apparatus as recited in claim 14 wherein the ESD circuit comprises a grounded gate NMOS transistor having a gate connected to ground.

20. The apparatus as recited in claim 1 wherein the ESD circuit comprises a grounded gate NMOS transistor having a gate connected to ground.

Assignees

• Silicon Lab Inc

Inventors

• Khazhinsky Michael G
• Kummaraguntla Ravi K

Classifications

• H02H3/202

  for DC systems · CPC title

• H02H9/04

  responsive to excess voltage (lightning arrestors H01C7/12, H01C8/04, H01G9/18, H01T) · CPC title

• H02H3/02

  Details · CPC title

• H02H9/046 Primary

  responsive to excess voltage appearing at terminals of integrated circuits · CPC title