Magnetically coupled signal isolator using a Faraday shielded MR or GMR receiving element

• US 6,054,780 A
• Filed: 07/17/1998
• Issued: 04/25/2000
• Est. Priority Date: 10/23/1997
• Status: Expired due to Term

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Haigh, Geoffrey T., Nickson, Paul R.
• Primary Examiner(s): PALADINI, ALBERT WILLIAM
• Application Number:
  US09/118,032
• Time in Patent Office: 648 Days
• Field of Search: 307/91, 307/89, 307/401, 338/32 H, 360/46, 360/113, 335/215, 324/207.21, 324/252, 330/62, 365/8, 365/158, 323/294, 323/368, 257/508, 257/660, 257/662, 257/659
• US Class Current: 307/91
• CPC Class Codes: H01L 2224/45099 Material
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/48137 the bodies being arranged next to each other, e.g. on a common substrate
• CPC Class Codes: H01L 23/5227 Inductive arrangements or effects of, or between, wiring layers other inductive arrangements H01L23/645
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H01L 2924/3025 Electromagnetic shielding
• CPC Class Codes: H04B 5/22 Capacitive coupling
• CPC Class Codes: H04B 5/73 for taking measurements, e.g. using sensing coils
• CPC Class Codes: H04B 5/75 for isolation purposes
• CPC Class Codes: H04L 25/0266 Arrangements for providing Galvanic isolation, e.g. by means of magnetic or capacitive coupling
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

An isolator having a driver circuit which responsive to an input signal drives appropriate signals into one or more coils which are magnetically coupled to one or more corresponding MR or GMR elements whose resistance is variable in response to the magnetic field applied by the coil(s), and an output circuit that converts the resistance changes to an output signal corresponding to the input signal. A Faraday shield is interposed between the coil(s) and the MR or GMR elements. Common mode transients applied to the driver are capacitively coupled from the coil(s) into the Faraday shield and therethrough to ground, instead of into the MR elements. A second Faraday shield may be disposed in spaced relationship with the first Faraday shield and referenced to the potential of the MR elements for even greater common mode rejection. The entire structure may be formed monolithically as an integrated circuit on a single substrate, for low cost, small size, and low power consumption. With proper driver and receiver circuits, the isolator may transmit either analog or digital signals.

Claims

1. A signal isolator comprising:

a. an input node for receiving an input signal;

b. at least one magnetic-field generation member actuable to generate a magnetic field corresponding to the input signal;

c. a magnetoresistive sensor positioned to receive and be influenced by the magnetic field generated by the at least one magnetic field generation member such that the sensor supplies at an output node a signal corresponding to the magnetic field; and

d. a Faraday shield disposed between the at least one magnetic-field generation member and the sensor, said shield being electrically referenced to a same potential as the output node, said referenced potential being galvanically isolated from a potential to which the input node is referenced.

2. The isolator of claim 1 wherein the magnetic-field generation member includes at least one coil which generates said magnetic field.

14. An isolator according to any of claims 1, 2, 3, 4, 6 or 8-13, further comprising, in addition to said Faraday shield, which shall be called the first Faraday shield, a second Faraday shield electrically referenced to a same potential as the input node and disposed between the at least one magnetic-field generation member and the first Faraday shield, the potential to which the input node is referenced and the potential to which the output node is referenced being galvanically isolated from each other.

3. A signal isolator, comprising:

a. an input node for receiving an input signal;

b. at least one magnetic-field generation member actuable to generate a magnetic field corresponding to the input signal;

c. a magnetoresistive sensor positioned to receive and be influenced by the magnetic field generated by the at least one magnetic field generation member, such that the sensor supplies at an output node a signal corresponding to the magnetic field; and

d. a Faraday shield disposed between the at least one magnetic-field generation member and the sensor, said shield being electrically referenced to a same potential as the output node;

wherein the magnetic-field generation member includes at least one coil which generates said magnetic field and a driver circuit coupled between the input node and the at least one coil and driving the at least one coil.

4. The isolator of claim 3 wherein the input signal is a digital signal, the at least one coil includes first and second coils, and the driver circuit drives the first and second coils with short pulses of current in response to logic value changes in the input signal.

5. The isolator of any of claims 3-4 further including a receiver circuit coupled to the sensor and supplying an output signal at an output thereof.

6. The isolator of claim 5 wherein the isolator is formed on a single semiconductor substrate.

7. The isolator of any of claims 3-4 wherein the isolator is formed on a single semiconductor substrate.

8. A signal isolator, comprising:

a. an input node for receiving an input signal;

b. at least one magnetic-field generation member actuable to generate a magnetic field corresponding to the input signal;

c. a magnetoresistive sensor positioned to receive and be influenced by the magnetic field generated by the at least one magnetic field generation member, such that the sensor supplies at an output node a signal corresponding to the magnetic field;

d. a Faraday shield disposed between the at least one magnetic-field generation member and the sensor, said shield being electrically referenced to a same potential as the output node; and

e. a receiver circuit coupled to the sensor and supplying an output signal at an output thereof;

wherein the magnetic-field generation member includes at least one coil which generates said magnetic field.

9. The isolator of claim 8, wherein the isolator is formed on a single semiconductor substrate.

10. A signal isolator, comprising:

a. an input node for receiving an input signal;

b. at least one magnetic-field generation member actuable to generate a magnetic field corresponding to the input signal;

c. a magnetoresistive sensor positioned to receive and be influenced by the magnetic field generated by the at least one magnetic field generation member, such that the sensor supplies at an output node a signal corresponding to the magnetic field; and

d. a Faraday shield disposed between the at least one magnetic-field generation member and the sensor, said shield being electrically referenced to a same potential as the output node;

wherein the magnetic-field generation member includes at least one coil which generates said magnetic field; and

wherein the isolator is formed on a single semiconductor substrate.

11. A signal isolator, comprising:

a. an input node for receiving an input signal;

b. at least one magnetic-field generation member actuable to generate a magnetic field corresponding to the input signal;

c. a magnetoresistive sensor positioned to receive and be influenced by the magnetic field generated by the at least one magnetic field generation member, such that the sensor supplies at an output node a signal corresponding to the magnetic field; and

d. a Faraday shield disposed between the at least one magnetic-field generation member and the sensor, said shield being electrically referenced to a same potential as the output node; and

e. a receiver circuit coupled to the sensor and supplying an output signal at an output thereof.

12. The isolator of claim 11, wherein the isolator is formed on a single semiconductor substrate.

13. A signal isolator, comprising:

a. an input node for receiving an input signal;

b. at least one magnetic-field generation member actuable to generate a magnetic field corresponding to the input signal;

c. a magnetoresistive sensor positioned to receive and be influenced by the magnetic field generated by the at least one magnetic field generation member, such that the sensor supplies at an output node a signal corresponding to the magnetic field; and

d. a Faraday shield disposed between the at least one magnetic-field generation member and the sensor, said shield being electrically referenced to a same potential as the output node;

wherein the isolator is formed on a single semiconductor substrate.