PROTECTION CIRCUIT

• US 20130308232A1
• Filed: 04/15/2013
• Published: 11/21/2013
• Est. Priority Date: 05/16/2012
• Status: Active Grant

• Current Assignee: NXP B.V. (NXP Semiconductors NV)
• Original Assignee: NXP B.V. (NXP Semiconductors NV)
• Inventors: ROUET, Pascal
• Granted Patent: US 9,083,175 B2
• Time in Patent Office: Days
• US Class Current: 361/56
• CPC Class Codes: G09G 2330/04 Display protection
• CPC Class Codes: G09G 2370/12 Use of DVI or HDMI protocol in interfaces along the display data pipeline
• CPC Class Codes: G09G 2380/10 Automotive applications
• CPC Class Codes: G09G 2380/12 Avionics applications
• CPC Class Codes: G09G 5/003 Details of a display terminal, the details relating to the control arrangement of the display terminal and to the interfaces thereto specific for a CRT G09G1/165; for a flat panel G09G3/2092
• CPC Class Codes: H02H 9/044 Physical layout, materials not provided for elsewhere varistors H01C7/12; spark-gaps H01T; Ovshinsky devices H10N70/00
• CPC Class Codes: H04L 25/02 Details ; arrangements for supplying electrical power along data transmission lines systems for transmitting signals via power distribution lines H04B3/54
• CPC Class Codes: H04L 25/06 Dc level restoring means; Bias distortion correction ; Decision circuits providing symbol by symbol detection

Abstract

HDMI devices coupled to interfaces in environments with high voltages, for example in an automotive vehicle, may be damaged by a short circuit between a cable and a large DC voltage. A protection circuit (100) for the high speed TMDS lines of an HDMI interface includes a DC voltage source (22, 24), a pair of capacitors (C1, C2) and a pair of splitters (12, 14). Each splitter is arranged to split a signal from respective one of the pair of electrical conductors between two signal paths, whereby one of the signal paths is coupled to the voltage source, and a second signal path is coupled to a first terminal of a respective one of the pair of capacitors. A signal received from an HDMI source (26) is split between a first path coupled to a first terminal of a respective capacitor and a second path coupled to the DC voltage source. The protection circuit can block a DC voltage on a cable (28) connected to the second terminals of the respective capacitors while providing a DC image of a receiver so allowing correct operation of a connected HDMI source.

Claims

1. A protection circuit for a High Definition Multimedia Interface (HDMI), the protection circuit comprising:

a pair of electrical conductors for carrying data transmitted as Transition Minimized Differential Signals,

a pair of capacitors, each said capacitor having a first terminal and a second terminal, wherein the first terminal of each said capacitor is coupled to a respective one of the pair of electrical conductors,

a voltage source operable to supply a DC voltage,

a pair of splitters, each said splitter being coupled to a respective one of the pair of electrical conductors and arranged to split a signal from a respective one of the pair of electrical conductors between at least two signal paths, wherein one of the at least two signal paths is coupled to the voltage source, and a second of the at least two signal paths is coupled to a first terminal of a respective one of the pair of capacitors, and wherein

in operation the protection circuit is arranged to couple the second terminal of each of the first and second capacitors to a cable for transmitting HDMI data, and wherein the protection circuit is operable to block a DC voltage in the cable from a High Definition Multimedia Interface source coupled to the pair of electrical conductors.

2. The protection circuit according to claim 1, wherein each of the splitters comprises:

a first resistor arranged in series between a respective one of the pair of electrical conductors and the first terminal of one of the pair of capacitors, and

a second resistor arranged between the first terminal of a respective one of the pair of capacitors and the voltage source.

4. The protection circuit according to claim 2, wherein a value of the first resistor is between 20 and 30 Ohms and a value of the second resistor is between 40 and 60 Ohms.

5. The protection circuit according to claim 2, wherein the supply voltage is in the range of 3 to 3.6 volts.

6. The protection circuit of claim 1 wherein the capacitance value is in a range of 0.25 nF to 2.0 nF.

7. The protection circuit according to claim 1, further comprising an ESD circuit arranged between the first terminal of each of the pair of capacitors and each of the pair of electrical conductors.

8. An HDMI source comprising at least one protection circuit according to claim 1, wherein at least one of a pair of TMDS outputs of the HDMI source are coupled to the respective pair of electrical conductors of the at least one protection circuit.

9. The HDMI source of claim 8, wherein the at least one of a pair of TMDS outputs is operable to output one of a differential data signal Of a differential clock signal.

10. An integrated circuit comprising the HDMI source according to claim 8.

11. A system for transmitting HDMI data, the system comprising:

the protection circuit of claim 1; and

a cable coupled to the second terminal of each of the pair of capacitors, the cable having a first end coupled to the second terminal of each of the pair of capacitors and a second end coupled to respective first terminals of a further pair of capacitors;

wherein

in operation the cable is arranged in series between an HDMI source coupled to the a pair of electrical conductors and an HDMI receiver coupled to the second terminal of the further pair of capacitors, and wherein the system is operable to protect the HDMI source and HDMI receiver from a DC voltage in the cable.

12. The system of claim 11, further comprising an HDMI source coupled to the pair of electrical conductors and an HDMI receiver coupled to the second terminal of the further pair of capacitors.

13. The system of claim 12, wherein the HDMI source comprises at least one of a portable device, an integrated circuit comprising an HDMI transmission circuit, a DVD player, a BluRay player, and a digital media server, and the HDMI receiver comprises at least one of a video display, and an integrated circuit comprising an HDMI receiver circuit.

14. A motor vehicle comprising the system of claim 11.

15. An aircraft comprising the system of claim 11.

3. The protection circuit according to claim wherein a value of the second resistor is twice a value of the first resistor.