Full-duplex communications over a single-wire bus

1. A single-wire bus apparatus comprising:

a single-wire bus consisting of one wire;

at least one slave circuit coupled to the single-wire bus and configured to:

cause a current variation on the single-wire bus during any of one or more bus symbols in a bus telegram to thereby communicate a first binary value over the single-wire bus; and

not cause the current variation on the single-wire bus during any of the one or more bus symbols in the bus telegram to thereby communicate a second binary value different from the first binary value over the single-wire bus; and

a master circuit comprising:

a bus driver circuit coupled to the single-wire bus and configured to:

communicate, concurrently over the single-wire bus, one or more voltage pulse-width modulation (PWM) values in the one or more bus symbols in the bus telegram, respectively; and

determine whether the current variation occurs on the single-wire bus in each of the one or more bus symbols; and

a receiver circuit coupled to the bus driver circuit and configured to, for each of the one or more bus symbols:

output the first binary value in response to detecting the current variation on the single-wire bus; and

output the second binary value in response to not detecting the current variation on the single-wire bus.

2. The single-wire bus apparatus of claim 1 wherein the bus driver circuit is further configured to modulate each of the one or more voltage PWM values by asserting a bus voltage at a lower bus voltage for a predefined low-voltage interval and raising the bus voltage to a higher bus voltage for a predefined high-voltage interval.

3. The single-wire bus apparatus of claim 2 wherein:

the bus driver circuit is further configured to:

communicate the one or more voltage PWM values in one or more read data symbols comprised in a read data frame; and

determine whether the current variation occurs in each of the one or more read data symbols; and

the receiver circuit is further configured to, for each of the one or more read data symbols:

output a binary one if the current variation occurs; and

output a binary zero if the current variation does not occur.

4. The single-wire bus apparatus of claim 3 wherein the first binary value and the second binary value outputted by the receiver circuit are unrelated to the one or more voltage PWM values communicated by the bus driver circuit.

5. The single-wire bus apparatus of claim 3 wherein each of the one or more voltage PWM values is equal to zero.

6. The single-wire bus apparatus of claim 3 wherein each of the one or more voltage PWM values is equal to one.

7. The single-wire bus apparatus of claim 3 wherein each of the one or more voltage PWM values is equal to the binary one or the binary zero last outputted by the receiver circuit.

8. The single-wire bus apparatus of claim 3 wherein each of the one or more voltage PWM values is equal to one or zero.

9. The single-wire bus apparatus of claim 3 wherein the at least one slave circuit comprises:

a slave port coupled to the single-wire bus;

a slave current sink coupled between the slave port and a ground;

a holding capacitor having a first end coupled to the slave port via a charge switch and a second end coupled to the ground; and

a slave controller coupled to the slave current sink and the charge switch.

10. The single-wire bus apparatus of claim 9 wherein the slave controller is configured to, for each of the one or more read data symbols:

determine whether to send the binary one or the binary zero;

deactivate the slave current sink during the predefined low-voltage interval and activate the slave current sink during the predefined high-voltage interval such that the at least one slave circuit draws a source current from the master circuit and thereby causes the current variation when the slave controller determines to send the binary one;

deactivate the slave current sink during the predefined low-voltage interval and the predefined high-voltage interval such that the at least one slave circuit does not draw the source current from the master circuit and thereby does not cause the current variation when the slave controller determines to send the binary zero;

close the charge switch during the predefined high-voltage interval such to charge the holding capacitor; and

open the charge switch during the predefined low-voltage interval.

11. The single-wire bus apparatus of claim 9 wherein:

the bus driver circuit is further configured to:

communicate any of the one or more voltage PWM values in a respective one of one or more acknowledgement (ACK) symbols succeeding a write data frame; and

determine whether the current variation occurs in the respective one of the one or more ACK symbols; and

the receiver circuit is further configured to:

output an indication indicating an ACK if the current variation occurs; and

output the indication indicating a No-ACK (NACK) if the current variation does not occur.

12. The single-wire bus apparatus of claim 11 wherein the any of the one or more voltage PWM values is modulated to indicate the ACK.

13. The single-wire bus apparatus of claim 11 wherein the slave controller is further configured to:

determine whether to send the ACK or the NACK during the any of the one or more ACK symbols;

activate the slave current sink in a first half of the any of the one or more ACK symbols and deactivate the slave current sink in a second half of the any of the one or more ACK symbols such that the at least one slave circuit draws a source current from the master circuit and thereby causes the current variation when the slave controller determines to send the ACK; and

deactivate the slave current sink such that the at least one slave circuit does not draw the source current from the master circuit and thereby does not cause the current variation when the slave controller determines to send the NACK.

14. The single-wire bus apparatus of claim 11 wherein the slave controller is further configured to:

determine whether to send the ACK or the NACK during the any of the one or more ACK symbols;

activate the slave current sink before a start of the any of the one or more ACK symbols and deactivate the slave current sink at the start of the any of the one or more ACK symbols such that the at least one slave circuit draws a source current from the master circuit and thereby causes the current variation when the slave controller determines to send the ACK; and

deactivate the slave current sink such that the at least one slave circuit does not draw the source current from the master circuit and thereby does not cause the current variation when the slave controller determines to send the NACK.

15. The single-wire bus apparatus of claim 2 wherein the master circuit further comprises:

a master port coupled to the single-wire bus;

a master current sink coupled between the master port and a ground; and

a master controller configured to cause the master circuit to modulate the one or more voltage PWM values in the one or more bus symbols, respectively.

16. The single-wire bus apparatus of claim 15 wherein:

the bus driver circuit comprises a master current source coupled to the master current sink and the master port; and

the master controller is further configured to, in each of the one or more bus symbols:

deactivate the master current source and activate the master current sink during the predefined low-voltage interval to assert the bus voltage at the lower bus voltage; and

activate the master current source and deactivate the master current sink during the predefined high-voltage interval to assert the bus voltage at the higher bus voltage.

17. The single-wire bus apparatus of claim 16 wherein the receiver circuit comprises:

a comparator coupled to the master port and configured to:

compare the bus voltage against a threshold voltage during the predefined high-voltage interval; and

output an indication signal that indicates whether the bus voltage is lower than the threshold voltage; and

a D type flip flop coupled to the comparator and configured to:

output the first binary value when the indication signal indicates that the bus voltage is lower than the threshold voltage; and

output the second binary value when the indication signal indicates that the bus voltage is not lower than the threshold voltage.

18. The single-wire bus apparatus of claim 15 wherein:

the bus driver circuit comprises a low dropout (LDO) master current source coupled to the master current sink and the master port; and

the master controller is further configured to:

deactivate the LDO master current source and activate the master current sink during the predefined low-voltage interval to assert the bus voltage at the lower bus voltage; and

activate the LDO master current source and deactivate the master current sink during the predefined high-voltage interval to maintain the bus voltage at a reference voltage substantially close to the higher bus voltage.

19. The single-wire bus apparatus of claim 18 wherein the LDO master current source comprises:

a transistor having a gate electrode configured to receive a gate voltage, a source electrode configured to receive a supply voltage, and a drain electrode coupled to the master port and configured to assert the bus voltage on the single-wire bus; and

a reference comparator having a first input configured to receive the reference voltage, a second input coupled to the drain electrode to receive the bus voltage, and an output coupled to the gate electrode and configured to output the gate voltage;

wherein the reference comparator is configured to reduce the gate voltage when the bus voltage is lower than the reference voltage to thereby maintain the bus voltage at the reference voltage.

20. The single-wire bus apparatus of claim 19 wherein the receiver circuit comprises:

a comparator coupled to the output of the reference comparator and configured to:

compare the gate voltage against a threshold voltage; and

output an indication signal that indicates whether the gate voltage is lower than the threshold voltage; and

a D type flip flop coupled to the comparator and configured to:

output the first binary value when the indication signal indicates that the gate voltage is lower than the threshold voltage; and

output the second binary value when the indication signal indicates that the gate voltage is not lower than the threshold voltage.