Signal isolator system with protection for common mode transients

• US 9,998,301 B2
• Filed: 11/03/2014
• Issued: 06/12/2018
• Est. Priority Date: 11/03/2014
• Status: Active Grant

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Yun, Ruida, Chen, Baoxing
• Primary Examiner(s): Leja, Ronald W
• Application Number:
  US14/531,141
• Publication Number:
  US 20160126724A1
• Time in Patent Office: 1,317 Days
• Field of Search: 361111
• CPC Class Codes: H04L 25/0266 Arrangements for providing Galvanic isolation, e.g. by means of magnetic or capacitive coupling
• CPC Class Codes: H04L 25/0276 Arrangements for coupling common mode signals

Abstract

An isolator system has an isolator that generates differential isolator signals and a receiver that generates digital data representative of signals received from the isolator. The system also may include an RC filter coupled between the isolator and the receiver. During operation, the filter may distribute transient signals across various circuit paths in the isolator, only some of which are coupled to the receiver inputs. Over time, the filter may attenuate transient contributions at the receiver inputs. In this manner, the filter may limit effects of these common mode transients.

Claims

1. An isolator system, comprising:

an isolator configured to generate differential isolator signals;

a receiver configured to generate digital data representative of signals received via the isolator; and

an RC filter coupled to the isolator and the receiver, wherein the RC filter comprises;

an input impedance stage extending between a first pair of terminals and having an intermediate node for connection to a first common mode reference voltage;

a second impedance stage extending between a second pair of terminals and having an intermediate node for connection to a second common mode reference voltage;

a voltage divider extending between a pair of supply voltages; and

a capacitor having a first terminal coupled to both an intermediate node of the voltage divider and the intermediate node of the second impedance stage, and having a second terminal coupled to one of the pair of supply voltages.

2. The system of claim 1, wherein the capacitor is a first capacitor and wherein the filter further comprises a pair of second and third capacitors, each connected between a respective terminal of the input impedance stage and a respective terminal of the second impedance stage.

3. The system of claim 1, wherein the intermediate node of the voltage divider is connected to the second impedance stage as the second common mode reference voltage.

4. The system of claim 1, wherein the filter comprises:

a high pass path coupling the first pair of terminals of the filter to input terminals of the receiver.

5. The system of claim 1, wherein the isolator comprises a transformer.

6. The system of claim 1, wherein the isolator comprises a pair of capacitors.

7. The system of claim 1, wherein the isolator comprises a magneto-resistor.

8. The system of claim 1, further comprising a transmitter coupled to the isolator, wherein the transmitter is an on-off key modulator.

9. The system of claim 1, further comprising a transmitter coupled to the isolator, wherein the transmitter is a pulse-count modulator.

10. The system of claim 1, further comprising a transmitter coupled to the isolator, wherein the transmitter is a pulse-polarity modulator.

11. The system of claim 1, wherein the isolator, filter, and receiver are provided on a common substrate.

12. The system of claim 1, wherein the isolator is provided on a first substrate and the filter and the receiver are provided on a second substrate.

13. The isolator system of claim 1, wherein the second pair of terminals represents input terminals of the receiver.

14. A filter for an isolator system, comprising:

an input impedance stage extending between a first pair of terminals and having an intermediate node for connection to a first common mode reference voltage;

a second impedance stage extending between a second pair of terminals and having an intermediate node for connection to a second common mode reference voltage;

a voltage divider extending between a pair of supply voltages;

a pair of capacitors, each connected between a respective terminal of the input impedance stage and a respective terminal of the second impedance stage; and

a third capacitor coupled between an intermediate node of the voltage divider and one of the pair of supply voltages.

15. The filter of claim 14, wherein the second pair of terminals are output terminals of the filter.

16. The filter of claim 14, wherein a capacitance of the third capacitor is at least twice a capacitance of each of the pair of capacitors.

17. The filter of claim 14, wherein the voltage divider comprises a pair of series-connected resistors.

18. The filter of claim 14, wherein the input impedance stage and the second impedance stage each comprise a respective pair of series-connected resistors.

19. A method, comprising:

biasing, at a first common mode voltage, a circuit path coupled between inputs of a receiver using a voltage divider extending between a pair of supply voltages;

biasing, at a second common mode voltage, a circuit path coupled between terminals coupled to an isolator producing a received isolator signal; and

responsive to onset of a common mode transient signal in the received isolator signal, holding the first common mode voltage at a value between the pair of supply voltages using a capacitor coupled between an intermediate node of the voltage divider and one of the pair of supply voltages.