Communication device and communication system

1. A communication device to be used as a master node in a communication system configured to use a pulse width modulation signal as transmission code among a plurality of nodes connected to a communication line, the communication device comprising:

a transmission transistor configured to be connected to the communication line;

a detector configured to detect a variation in current during an on-period of the transmission transistor; and

a communication circuit configured to determine off-timing of the transmission transistor based on timing of occurrence of the variation in current, wherein

the timing of occurrence of the variation in current corresponds to on-timing of a second transmission transistor provided in a slave node, and

the communication circuit is configured to determine the off-timing of the transmission transistor such that a simultaneously-on period TB of the transmission transistor and the second transmission transistor fulfills TB=(2n−1)/2f, where f is a frequency of electromagnetic interference (EMI) noise and n is a natural number.

2. The communication device according to claim 1 , wherein the detector is provided in a current path via the transmission transistor.

3. The communication device according to claim 1 , wherein the detector includes:

a current-voltage conversion element configured to convert a current signal into a voltage signal; and

a comparator configured to compare the voltage signal with a predetermined threshold value.

4. The communication device according to claim 1 , further comprising:

a receiver connected to the communication line; and

a waveform shaper configured to control a drive signal for the transmission transistor.

5. A communication system including a master node, a slave node, and a communication line, the communication system using a pulse width modulation signal as transmission code between the master node and the slave node, which are connected to the communication line, wherein

the master node is the communication device according to claim 1 .

6. The communication system according to claim 5 , wherein a terminal resistor in the master node has a lower resistance value than a terminal resistor in the slave node.

7. The communication system according to claim 6 , wherein

the communication system complies with a clock extension peripheral interface (CXPI) protocol.

8. A vehicle comprising the communication system according to claim 5 .

9. A communication device to be used as a slave node in a communication system configured to use a pulse width modulation signal as transmission code among a plurality of nodes connected to a communication line, the communication device comprising:

a transmission transistor connected to the communication line;

a detector configured to monitor a pulse width when only a master node is keeping the pulse width modulation signal at a dominant level; and

a waveform shaper configured to control a drive signal for the transmission transistor in accordance with an output of the detector.

10. The communication device according to claim 9 , wherein

the detector is configured to compare the pulse width with a predetermined threshold value.

11. The communication device according to claim 10 , wherein

the waveform shaper is configured such that, at an on-transition of the transmission transistor,

if the pulse width detected prior to the on-transition is greater than the threshold value, the waveform shaper controls the drive signal so as to limit a bus current passing across the communication line and,

if the pulse width is smaller than the threshold value, the waveform shaper controls the drive signal so as not to limit the bus current.

12. The communication device according to claim 11 , wherein

the waveform shaper is configured such that, at an on-transition of the transmission transistor,

when limiting the bus current, the waveform shaper turns the drive signal to a logic level corresponding to an on-period at a first slew rate and,

when not limiting the bus current, the waveform shaper turns the drive signal to the logic level corresponding to the on-period at a second slew rate higher than the first slew rate.

13. The communication device according to claim 12 , wherein

the waveform shaper includes:

a first waveform shaper configured to turn the drive signal to the logic level corresponding to the on-period at the first slew rate;

a second waveform shaper configured to turn the drive signal to the logic level corresponding to the on-period at the second slew rate; and

a selector configured to enable one of the first and second waveform shapers in accordance with the output of the detector.

14. The communication device according to claim 9 , wherein

the waveform shaper includes a current source configured to generate an on-current for turning the drive signal to a logic level corresponding to an on-period, and is configured to control a magnitude of the on-current in accordance with the output of the detector.

15. The communication device according to claim 9 , further comprising:

a receiver and a terminal resistor that are connected to the communication line; and

a communication circuit that is connected to the detector, to the waveform shaper, and to the receiver.

16. A communication system including a master node, a slave node, and a communication line, the communication system using a pulse width modulation signal as transmission code between the master node and the slave node, which are connected to the communication line, wherein

the slave node is the communication device according to claim 9 .

17. The communication system according to claim 16 , wherein

a terminal resistor in the master node has a lower resistance value than a terminal resistor in the slave node.

18. A vehicle comprising the communication system according to claim 16 .