FPD-Link - FPD-Link III

FPD-Link III was introduced in 2010. Further improving FPD-Link II, FPD-Link III's major feature is embedding a bidirectional communication channel on the same differential pair. This bidirectional channel transfers control signals between source and destination in addition to the clock and streaming video data. Therefore, FPD-Link III even further reduces cable cost by eliminating cables for control channels such as I2C and CAN bus.

FPD-Link III's embedded control channel uses the I2C bus protocol between the source and destination in the first implementations. (However, it is not limited to I2C.) The I2C master can read and write to all the slaves on the other side of the FPD-Link III chipset, which is effectively transparent to the I2C master and slaves communications. For example, this enables infotainment head units to control and configure displays, and image processing units to control and configure cameras using the same twisted pair cable as the data transmission.

The Digital Content Protection LLC approved FPD-Link III in 2009 as a high-bandwidth interface for carrying content whose owner wants HDCP security. This approval enables the FPD-Link III chipsets to include the highly-confidential HDCP keys and state machines to encrypt the content. The embedded control channel in the FPD-Link III chipsets simplifies the key exchange protocols between the source and destinations that verify the destination is secure.

An additional new feature, FPD-Link III stops using LVDS technology and uses only CML for the serialized high-speed signals. This enables it to easily work at data rates greater than 3 Gbit/s on cables greater than 10m long. An additional benefit for using CML is the coax-cable drive capability. The CML technology works well when driving the single conductor in coax cables. Since coax cables are very good at controlling impedance and noise, they reduce the need for differential signaling, which better tolerates impedance discontinuities and noise interference.

Another added benefit for FPD-Link III is the adaptive equalization built into the deserializer. The input signal to the deserializer usually has diminished integrity. This typically results from the ISI due to cable loss. The adaptive equalizer can sense the poor signal and restore it to the original integrity. This feature is useful in every application where the cable can vary in length, operating temperature, and humidity because these variables affect the ISI resulting from the low-pass filer affect of the cable.