Programmable cable with deskew and performance analysis circuits
An HDMI cable carries high speed encoded data which are transmitted differentially over data channels, along with a clock. High-frequency loss and differential skew within a differential signal may be compensated by analog circuits embedded in the cable. These embedded circuits are tuned at production for best performance by observing the quality of the recovered analog signal. The embedded circuits are powered by a combination of power sources, both carried within the cable, and harvested from the high-speed signals themselves.
1. A cable for connecting a transmitting data source device to a receiving data sink device carrying differential signals, the cable including:
a basic cable operably connected to a boost device for boosting at least one of differential signals;
the boost device comprising:
an input circuit for receiving a raw differential signal from the data source device and outputting a recovered signal;
a deskew circuit with adjustable parameters for processing the recovered signal into a deskewed signal;
an output circuit for amplifying the deskewed signal into a boosted signal and sending the boosted signal to the data sink device;
wherein the boost device further includes:
a parameter memory for retaining the adjustable parameters after they have been adjusted; and
a performance analysis circuitry for determining the performance of the cable.
2. The cable as described in claim 1 , wherein the basic cable further includes a control bus, and wherein the parameter memory is accessible from said control bus.
3. The cable as described in claim 2 , wherein the boost device further includes an equalizer circuit for adjusting the frequency response of the deskewed signal.
4. The cable as described in claim 3 , wherein the performance analysis circuitry includes:
a differential to single-ended block for converting the boosted signal to a single-ended signal;
an oversampling circuit providing a digital representation of the single ended signal to generate a preprocessed data signal; and
a training function circuit for estimating a quality of the preprocessed data signal, and adjusting the parameters of the deskew and equalizer circuitry by changing the adjustable parameters to improve quality of the preprocessed data signal.
5. The cable as described in claim 4 , wherein the training function circuit further comprises:
a digital circuit for estimating the quality of the preprocessed data signal and generating a Quality Number indicating said quality;
an evaluation run control circuit for adjusting the parameters of the deskew and equalizer circuitry to a number of predetermined settings, and for monitoring a predetermined number of
the oversampled bits for each setting;
a memory for retaining the best setting corresponding to the highest Quality Number; and
a means for updating the said parameters to the best setting.
6. The cable as described in claim 5 , wherein the performance analysis circuitry includes means for receiving a start trigger to the evaluation run control circuit and reporting the best setting over the control bus.
7. The cable as described in claim 5 , wherein the digital circuit for estimating the quality comprises:
a length detection circuit for determining the run length of contiguous “1” or “0” samples in the digital representation of the preprocessed data signal within a window of at least one bit period;
a plurality of counters for counting the number of occurrences of selected run lengths during an observation period of “N” bits; and
a bit quality calculator for processing the outputs of the counters into the Quality Number indicating the quality of the preprocessed data signal.
8. A boost device for a cable connecting a transmitting data source device to a receiving data sink device, the transmitting data source device sending differential data signals into the boost device, the boost device boosting at least one of the differential data signals, the boost device comprising:
an input circuit for receiving a raw differential signal from the data source device and outputting a recovered signal;
a deskew circuit with adjustable parameters for processing the recovered signal into a deskewed signal;
an output circuit for amplifying the deskewed signal into a boosted signal and sending the boosted signal to the data sink device;
wherein the boost device further includes:
a parameter memory for retaining the adjustable parameters; and
performance analysis circuitry for determining the performance of the cable.
9. The boost device as described in claim 8 , further including a control input for accessing the parameter memory from a control bus carried in the cable.
10. The boost device as described in claim 9 , further comprising an equalizer circuit for adjusting the frequency response of the deskewed signal.
11. The boost device as described in claim 8 , wherein the performance analysis circuitry includes:
a differential to single-ended block for converting the boosted signal to a single-ended signal;
an oversampling circuit providing a digital representation of the single ended signal to generate a preprocessed data signal; and
a training function circuit for estimating a quality of the preprocessed data signal, and adjusting the parameters of the deskew and equalizer circuitry by changing the adjustable parameters to improve quality of the preprocessed data signal.
12. The boost device as described in claim 11 , wherein the training function circuit further comprises:
a digital circuit for estimating the quality of the preprocessed data signal and generating a Quality Number indicating said quality;
an evaluation run control circuit for adjusting the parameters of the deskew and equalizer circuitry to a number of predetermined settings, and for monitoring a predetermined number of
the oversampled bits for each setting;
a memory for retaining the best setting corresponding to the highest Quality Number; and
a means for updating the said parameters to the best setting.
13. The boost device as described in claim 12 , wherein the performance analysis circuitry includes means for receiving a start trigger to the evaluation run control circuit and reporting the best setting over the control input.
14. A method for determining the performance of a cable comprising a boost device, the method comprising:
receiving a differential data signal;
deskewing and equalizing the differential data signal according to adjustable parameters;
outputting a boosted signal;
the boost device comprising a performance analysis circuitry;
converting the boosted signal to a single-ended signal;
oversampling the single ended signal to generate a preprocessed data signal;
estimating a quality of the preprocessed data signal; and
adjusting the adjustable parameters to improve the quality of the preprocessed data signal.
15. The method as described in claim 14 , further comprising an evaluation run step including:
estimating the quality of the preprocessed data signal and generating a Quality Number indicating said quality;
adjusting the adjustable parameters to a number of predetermined settings;
monitoring the preprocessed data signal for each setting;
retaining the best setting corresponding to the highest Quality Number; and
updating the adjustable parameters to the best setting.
16. The method as described in claim 15 , further comprising:
starting the evaluation run step by receiving a start trigger; and
reporting the best setting over a control bus to a parameter memory in the cable.