Isolated communications interface

• US 8,908,779 B2
• Filed: 04/27/2012
• Issued: 12/09/2014
• Est. Priority Date: 04/29/2011
• Status: Active Grant

• Current Assignee: Analog Devices International Unlimited Company (Analog Devices, Inc.)
• Original Assignee: Linear Technology Corporation (Analog Devices, Inc.)
• Inventors: Douglass, James Michael
• Primary Examiner(s): FILE, ERIN M
• Application Number:
  US13/458,765
• Publication Number:
  US 20120275527A1
• Time in Patent Office: 956 Days
• Field of Search: 375/257, 375/258
• US Class Current: 375/257
• CPC Class Codes: H04L 25/0272 Arrangements for coupling to multiple lines, e.g. for differential transmission
• CPC Class Codes: H04L 25/0278 Arrangements for impedance matching

Abstract

A method and interface for serial communication is provided. The interface includes a differential input/output having a first node and a second node. There are several input/output nodes arranged to receive serial interface signals. The interface includes a transmitter configured to drive a twisted pair cable at the differential input/output. There is a receiver coupled to the differential input/output that includes a window comparator. A serial port control unit provides serial data to the transmitter and receives serial data from the receiver. The serial communications interface transmits serial data to and receives serial data from a second serial communications interface independent of a reference clock and is galvanically isolated from the second serial communications interface.

Claims

1. A serial communications interface, comprising:

a differential input/output having a first node and a second node;

a plurality of input/output nodes arranged to receive serial interface signals;

a transmitter configured to drive a twisted pair cable at the differential input/output;

a receiver coupled to the differential input output, the receiver comprising a window comparator; and

a serial port controller unit coupled to the serial interface input/output nodes, the transmitter, and the receiver;

wherein;

the serial port controller unit is configured to provide serial data to the transmitter and receive serial data from the receiver;

the transmitter and the twisted pair cable are on opposite sides of the galvanic isolation;

the serial port controller, the receiver, and the transmitter are on the same side of the galvanic isolation; and

the serial communications interface is;

configured to transmit serial data to and receive serial data from a second serial communications interface one data bit at a time, without a clock reference sent with or embedded in the serial data; and

configured to be galvanically isolated from the second serial communications interface.

2. The serial communications interface of claim 1, wherein the serial communications interface is bidirectional.

3. The serial communications interface of claim 1, wherein the transmitter comprises a differential current driver including:

a first current source;

a second current source;

a first switch configured to pull up the first node by providing a path from the first current source to the first node;

a second switch configured to pull up the second node by providing a path from the first current source to the second node;

a third switch configured to pull down the first node by providing a path from the second current source to the first node; and

a fourth switch configured to pull up the second node by providing a path from the second current source to the second node.

4. The serial communications interface of claim 3, wherein the transmitter is configured to drive the twisted pair cable through a galvanic isolator.

5. The serial communications interface of claim 3, wherein the transmitter is configured to provide a 0 level at the differential output when both the first and second current sources are turned OFF.

6. The serial communications interface of claim 1, wherein the serial communications interface is configured to communicate as a master serial communications interface when a master node is tied to a first voltage level and as a slave serial communications interface when tied to a second voltage level.

7. The serial communications interface of claim 6, wherein the serial communications interface is configured to:

be controlled by a master device when configured to communicate as the master serial communications interface; and

control a slave device when configured to communicate as the slave serial communications interface.

8. The serial communications interface of claim 1, wherein the serial communications interface is galvanically isolated from the second serial communications interface through at least one of magnetic coupling and capacitive coupling.

9. The serial communications interface of claim 1, further comprising:

a clock phase input node (PHA); and

a clock polarity input node (POL), wherein the serial communications interface is configured to;

in a first mode;

provide positive pulses to a master microcontroller and latch the serial data on a rising clock edge;

in a second mode;

provide positive pulses to the master microcontroller and latch the serial data on a falling clock edge;

in a third mode;

provide negative pulses to the master microcontroller and latch the serial data on a rising clock edge; and

in a fourth mode;

provide negative pulses to the master microcontroller and latch the serial data on a falling clock edge.

10. The serial communications interface of claim 9, wherein the serial communications interface is:

in a first mode when the POL node is at a first digital voltage level and the PHA node is at the first digital voltage level;

in a second mode when the POL node is at the first digital voltage level and the PHA node is at a second digital voltage level;

in a third mode when the POL node is at the first digital voltage level and the PHA node is at the first digital voltage level; and

in a fourth mode when the POL node is at the first digital voltage level and the PHA node is at the second digital voltage level.

11. A serial communication method, comprising:

receiving serial interface signals on a first set of input nodes;

driving a twisted pair cable differentially at output nodes, the output nodes comprising a first node and a second node;

transmitting serial data to and receiving serial data from a remote serial communications interface one data bit at a time, without a clock reference sent with or embedded in the serial data;

galvanically isolating the transmitted signals from the remote serial communications interface;

operating the transmitter and the twisted pair cable on opposite sides of the galvanic isolation; and

operating the transmitter and the receiver on the same side of the galvanic isolation.

12. The serial communication method of claim 11, further comprising transferring the data over the twisted pair cable bidirectionally.

13. The serial communication method of claim 11, wherein the transmitting serial data includes:

pulling up the first node by providing a path from a first current source to the first node;

pulling up the second node by providing a path from the first current source to the second node;

pulling down the first node by providing a path from a second current source to the first node; and

pulling up the second node by providing a path from the second current source to the second node.

14. The serial communication method of claim 13, wherein driving the twisted pair cable at the differential output is through a galvanic isolator.

15. The serial communication method of claim 13, further comprising providing a 0 level at the output nodes when both the first and second current sources are turned OFF.

16. The serial communication method of claim 11, further comprising communicating as a master serial communications interface when a master node is tied to a first voltage level and as a slave serial communications interface when tied to a second voltage level.

17. The serial communication method of claim 16, further comprising:

receiving control instructions from a master device when configured to communicate as the master serial communications interface; and

controlling a slave device when configured to communicate as the slave serial communications interface.

18. The serial communication method of claim 11, wherein galvanically isolating from the remote serial communications interface is through at least one of magnetic coupling and capacitive coupling.

19. The serial communication method of claim 11, further comprising:

in a first mode;

providing positive pulses to a master microcontroller and latching the serial data on a rising clock edge;

in a second mode;

providing positive pulses to a master microcontroller and latching the serial data on a falling clock edge;

in a third mode;

providing negative pulses to the master microcontroller and latching the serial data on a rising clock edge; and

in a fourth mode;

providing negative pulses to the master microcontroller and latching the serial data on the falling clock edge.

20. The serial communication method of claim 19, further comprising:

operating in a first mode when a clock polarity input (POL) node is at a first digital voltage level and a clock phase input node (PHA) node is at the first digital voltage level;

operating in a second mode when the POL node is at the first digital voltage level and the PHA node is at a second digital voltage level;

operating in a third mode when the POL node is at the first digital voltage level and the PHA node is at the first digital voltage level; and

operating in a fourth mode when the POL node is at the first digital voltage level and the PHA node is at the second digital voltage level.