Automatic threshold adjustment for USB power delivery to work with cables out of specification
An apparatus includes a bi-phase mark coded (BMC) input port configured to receive BMC signals from a universal serial bus (USB) cable. The apparatus further includes a threshold adjustment circuit configured to generate a threshold, and a comparator configured to compare an input BMC signal from the BMC input port and the threshold and based on the comparison, generate an adjusted input BMC signal. The threshold adjustment circuit is further configured to adjust the threshold based upon the input BMC signal.
1. An apparatus, comprising:
a bi-phase mark coded (BMC) input port to receive BMC signals from a universal serial bus (USB) cable;
a threshold adjustment circuit to generate a voltage threshold;
and
a comparator to:
compare an input BMC signal from the BMC input port and the voltage threshold; and
based on the comparison, generate an adjusted input BMC signal;
wherein the threshold adjustment circuit is to
adjust the voltage threshold based upon the input BMC signal through evaluation of the adjusted input BMC signal;
determine whether the adjusted input BMC signal is idle; and
based on a determination that the adjusted input BMC is idle, adjust the voltage threshold to an estimated voltage threshold value.
2. The apparatus of claim 1 , wherein the threshold adjustment circuit is to adjust the voltage threshold based upon relative durations of logic high signals and logic low signals over a defined time length of the input BMC signal.
3. The apparatus of claim 2 , wherein the threshold adjustment circuit is to raise or lower the voltage threshold until the durations of logic high signals and logic low signals over a defined time length of the input BMC signal are approximately equal.
4. The apparatus of claim 3 , wherein the defined time length is four bits of the input BMC signal.
5. The apparatus of claim 1 , wherein threshold adjustment circuit is to determine the estimated voltage threshold value by incrementally adjusting the voltage threshold until the adjusted input BMC is no longer idle.
6. The apparatus of claim 1 , wherein threshold adjustment circuit is to:
determine a current passing through the USB cable;
determine an impedance of the USB cable; and
determine the estimated voltage threshold value by a calculation of a voltage resulting from the current and the impedance.
7. A method, comprising:
receiving bi-phase mark coded (BMC) signals at a BMC input port from a universal serial bus (USB) cable;
generating a voltage threshold;
comparing an input BMC signal from BMC input port and the voltage threshold;
based on the comparison, generating an adjusted input BMC signal;
adjusting the voltage threshold based upon the input BMC signal;
determining whether the adjusted input BMC signal is idle; and
based on a determination that the adjusted input BMC is idle, adjusting the voltage threshold to an estimated voltage threshold value;
wherein adjusting the voltage threshold based on the input BMC signal includes evaluating the adjusted input BMC signal.
8. The method of claim 7 , wherein the voltage threshold is adjusted based upon relative durations of logic high signals and logic low signals over a defined time length of the input BMC signal.
9. The method of claim 8 , wherein the voltage threshold is adjusted by raising or lowering the voltage threshold until the durations of logic high signals and logic low signals over a defined time length of the input BMC signal are approximately equal.
10. The method of claim 9 , wherein the defined time length is four bits of the input BMC signal.
11. The method of claim 7 , comprising determining the estimated voltage threshold value by incrementally adjusting the voltage threshold until the adjusted input BMC is no longer idle.
12. The method of claim 7 , comprising:
determining a current passing through the USB cable;
determining an impedance of the USB cable; and
determining the estimated voltage threshold value by calculated the voltage resulting from the current and the impedance.
13. A universal serial bus (USB) element, comprising:
a bi-phase mark coded (BMC) input port to receive BMC signals from a USB cable;
a threshold adjustment circuit to generate a voltage threshold; and
a comparator to:
compare an input BMC signal from the BMC input port and the voltage threshold; and
based on the comparison, generate an adjusted input BMC signal;
wherein the threshold adjustment circuit is to;
adjust the voltage threshold based upon the input BMC signal through evaluation of the adjusted input BMC signal;
determine whether the adjusted input BMC signal is idle; and
based on a determination that the adjusted input BMC is idle, adjust the voltage threshold to an estimated voltage threshold value.
14. The USB element of claim 13 , wherein the threshold adjustment circuit is to adjust the voltage threshold based upon relative durations of logic high signals and logic low signals over a defined time length of the input BMC signal.
15. The USB element of claim 14 , wherein the threshold adjustment circuit is to raise or lower the voltage threshold until the durations of logic high signals and logic low signals over a defined time length of the input BMC signal are approximately equal.