Physical Layer - CAN System Engineering - page 49

Fig. 2.4 Typical signal for a high-speed CAN physical layer
Figure 2.4 shows a typical high-speed CAN bus signal.
High-Speed Transceiver
Two different kinds of transceivers are in the market now:
• ISO 11898-2 transceiver
• ISO 11898-5 transceiver, with remote wake-up feature
The typical high-speed CAN transceiver consists of a transmitter and a receiver.
Two 20-kΩ resistors, connected to an internal voltage source of 2.5 V , stabilize
the bus voltage to 2.5 V in recessive state. The receiver is a differential comparator
with electromagnetic compatibility (EMC) filter. This comparator monitors the bus
levels and transforms the differential signal of the bus levels to a logic signal on
pin RxD. High level on RxD is recessive level on the bus and low level on RxD is
dominant level on the bus.
Figure 2.5 shows a block diagram of an ISO 11898-2 transceiver (left) and the
ISO 11898-5 transceiver with remote wake-up (right).
Transceiver according to ISO 11898-2
A transceiver according to ISO 11898-2 is a transceiver with a transmitter and a re-
ceiver to transmit and receive data only. In the first generation of this kind of trans-
ceiver, no additional function was implemented. In newer generations, the ESD
robustness is dramatically increased up to 15 kV and the emission is reduced to very