Self calibrating cable for a high definition digital video interface
An HDMI cable may exhibit frequency dependent signal attenuation, inter symbol interference, and inter-pair skew. A boost device integrated with the cable can compensate for such impairments of the cable. A self calibrating cable with a boost device of the embodiment of the invention is described, in which parameters that control the response of the boost device are set optimally in a self-calibrating process including looping the boosted cable on itself through a calibration fixture that contains a calibration control device. The boost device includes pattern generators and a sampling circuit. Each high speed channel of the cable is separately tested and calibrated with the help of one of the other channels serving as a sampling channel.
1. A method for calibrating a high speed cable having a boost device embedded in the cable, the cable carrying a plurality of two or more high speed channels and a low speed control bus, the cable including an input connector and an output connector, the boost device having programmable parameters, the method comprising:
(a) looping the high speed channels from the output connector to the input connector outside the high-speed cable;
(b) selecting a test channel from among the high speed channels;
(c) selecting a sampling channel from among the remaining high speed channels; and
(d) calibrating the test channel using the sampling channel, including adjusting the programmable parameters of the boost device.
2. The method of claim 1 , further comprising repeating the steps (b) to (d) until all high speed channels are calibrated.
3. The method of claim 1 , wherein the step (b) comprises:
coupling a data pattern generator to the test channel; and
sending a data pattern from the data pattern generator on the test channel to the output connector.
4. The method of claim 1 , wherein the step (c) comprises:
coupling a sampling pattern generator to the sampling channel; and
sending a sampling pattern from the sampling pattern generator on the sampling channel to the output connector.
5. The method of claim 1 , wherein the step (a) further comprises coupling each of the high speed channels from the input connector through wires of the high speed cable to an input of a respective programmable boost circuit of the boost device.
6. The method of claim 5 , wherein the step (d) comprises:
(1) programming a delay of a first programmable boost circuit associated with the test channel;
(2) receiving the test channel carrying the test pattern at the first programmable boost circuit;
(3) receiving the sampling channel carrying the sampling pattern at a second programmable boost circuit associated with the sampling channel; and
(4) sampling an output of the first programmable boost circuit with an output of the second programmable boost circuit to determine a signal quality of the test pattern of the received test channel.
7. The method of claim 6 , further comprising repeating steps (1) to (4) with different delays until a satisfactory signal quality is achieved, thereby calibrating the test channel.
8. The method of claim 7 , further comprising repeating the steps (b) to (d) until all high speed channels are calibrated.
9. The method of claim 1 , wherein the high speed cable is a High-Definition Multimedia Interface (HDMI) cable.
10. A system for calibrating a high speed cable, carrying a plurality of two or more high speed channels and a low speed control bus, the cable having an input connector and an output connector, the system comprising:
a calibration fixture for looping the high speed channels from the output connector to the input connector outside the high-speed cable;
a boost device embedded in the cable, the boost device being configured to select a test channel from among the high speed channels, and a sampling channel from among the remaining high speed channels;
a calibration circuit for calibrating the test channel using the sampling channel, the calibration circuit being operatively coupled to the low speed control bus; and
a calibration control device operatively coupled to the high-speed cable through the low speed control bus.
11. The system of claim 10 , wherein the calibration circuit comprises:
a sampling circuit for sampling the test channel with the sampling channel;
a parameter memory for storing programmable parameters of the boost device; and
a sampling control circuit for monitoring the sampling circuit and for setting the programmable parameters in the parameter memory.
12. The system of claim 10 , wherein the boost device comprises a plurality of channel circuits, each channel circuit including a programmable boost circuit for boosting a corresponding one of the high speed channels, the programmable boost circuit being responsive to programmable parameters of the boost device stored in a parameter memory.
13. The system of claim 12 , wherein:
each channel circuit further comprises a pattern generator; and
the boost device further comprises a low speed control bus interface, interfacing the low speed control bus for controlling the pattern generator of each channel circuit.
14. The system of claim 13 , wherein the boost device further comprises:
a first multiplexer coupled to the pattern generator of the channel circuit of the test channel for sending a test pattern on the test channel; and
a second multiplexer coupled to the pattern generator of the channel circuit of the sampling channel for sending a sampling pattern on the sampling channel.
15. The system of claim 12 , wherein the boost device comprises:
a data tap coupled to an output of the programmable boost circuit boosting the test channel; and
a sampling tap coupled to an output of the programmable boost circuit boosting the sampling channel.
16. The system of claim 15 , wherein:
the sampling circuit comprises:
a programmable delay for delaying an output of the sampling tap;
a sampling circuit element for generating binary samples from an output of the data tap clocked with the delayed output of the sampling tap;
the sampling circuit being configured to determine an average of N generated binary samples, which have a predetermined value; and
the calibration circuit comprises a sampling control circuit, which is configured to vary the programmable delay in predetermined delay steps.
17. The system of claim 15 , wherein the sampling control circuit further comprises a memory for storing some or all of the delay steps and corresponding averages.
18. The system of claim 10 , wherein the calibration control device is configured to interpolate between averages obtained by varying the programmable delay in the predetermined delay steps.
19. The system of claim 10 , wherein the calibration control device is a micro controller or a field programmable array.
20. The system of claim 10 , wherein the high speed cable is a High-Definition Multimedia Interface (HDMI) cable.
21. A self-calibrating high speed cable, carrying a plurality of two or more high speed channels and a low speed control bus, the cable having an input connector and an output connector, the cable comprising:
a boost device embedded in the cable, the boost device being configured to select a test channel from among the high speed channels, and a sampling channel from among the remaining high speed channels; and
a calibration circuit for calibrating the test channel using the sampling channel, the calibration circuit being operatively coupled to the low speed control bus.
22. The cable of claim 21 , wherein the calibration circuit comprises:
a sampling circuit for sampling the test channel with the sampling channel;
a parameter memory for storing programmable parameters of the boost device; and
a sampling control circuit for monitoring the sampling circuit and for setting the programmable parameters in the parameter memory.
23. The cable of claim 21 , wherein the boost device comprises a plurality of channel circuits, each channel circuit including a programmable boost circuit for boosting a corresponding one of the high speed channels, the programmable boost circuit being responsive to programmable parameters of the boost device stored in a parameter memory.
24. The cable of claim 23 , wherein the boost device comprises:
a data tap coupled to an output of the programmable boost circuit boosting the test channel; and
a sampling tap coupled to an output of the programmable boost circuit boosting the sampling channel.
25. The cable of claim 24 , wherein:
the sampling circuit comprises:
a programmable delay for delaying an output of the sampling tap;
a sampling circuit element for generating binary samples from an output of the data tap clocked with the delayed output of the sampling tap;
the sampling circuit being configured to determine an average of N generated binary samples, which have a predetermined value; and
the calibration circuit comprises a sampling control circuit configured to vary the programmable delay in predetermined delay steps.
26. The cable of claim 25 , wherein the sampling control circuit further comprises a memory for storing some or all of the delay steps and corresponding averages.
27. The cable of claim 21 , wherein:
each channel circuit further comprises a pattern generator; and
the boost device further comprises a low speed control bus interface, interfacing the low speed control bus for controlling the pattern generator of each channel circuit.
28. The cable of claim 27 , wherein the boost device comprises:
a first multiplexer coupled to the pattern generator of the channel circuit of the test channel for sending a test pattern on the test channel; and
a second multiplexer coupled to the pattern generator of the channel circuit of the sampling channel for sending a sampling pattern on the sampling channel.
29. The cable of claim 21 , wherein the high speed cable is a High-Definition Multimedia Interface (HDMI) cable.