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Ethernet for ADAS: Addressing automotive challenges

07 Jan 2015  | Mike Jones

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The provision of standard DC-DC regulation is all that is needed for the camera power management solution (figure 4). A Micrel MIC28511 60Vin 3A Synchronous Buck Regulator with HyperLight Load technology provides the primary step down voltage and high efficiency operation in low output power operation, such as standby.


Figure 4: PoE with standard DC-DC regulation.


Standard Ethernet PoE for automotive applications still offers the additional benefits provided by the 'phantom supply' method, despite optimisation and cost benefits.

At the camera (PD side), common mode noise rejection is provided; any noise from the PSE (ECU) or picked up along the twisted–pair cable routing is coupled as common mode noise to the differential Ethernet signal and is removed.

In addition, the galvanic isolation between the camera (PD) and ECU (PSE) grounds prevents radiating ground loops occurring due to potentials differences; a common occurrence. Interoperability can also be achieved interfacing to any other IEEE 802.3af/at PSE.

100BASE-TX Ethernet already offers the lowest power PHY technology on the market today. When compared to Gigabit-based technology solutions, power and cost is up to three times lower.

The KSZ8061 support of IEEE 802.3az energy efficient Ethernet (EEE) offers another benefit to the camera, since during idle periods (i.e., when no video traffic is sent), the PHY can transition into a low power sleep mode.


Figure 5: KSZ8061 PHY.


This reduces power consumption by over 50 per cent. The KSZ8061 Ethernet PHY also provides an industry best of class, ultra-low standby current <1uA making it ideal for battery applications.

In addition, the KSZ8061 PHY exhibits a unique signal detect output pin, to signify the presence of an active link partner (figure 5). PHY standby mode can be activated and woken up automatically by the signal detection circuitry.

Furthermore, the output pin can be used to power down the processor and sensors by the power management, achieving remote sub-1uA standby and wakeup of the camera module.

This remote power down scheme offers key advantages:

 • Complete interoperability with any Ethernet vendor link partner PHY (at ECU)
 • Less standby power
The alternative method of special waveforms / sequences tends to require proprietary implementation, restricting its practical use.

A good example of this in the consumer world is the vendor driven wake-on-LAN (WoL) method, which in reality is rarely utilised the field. In terms of standby power, implementing a detection circuit at the physical layer requires less signal processing and thus consumes less power.

In this alternative example, WoL would still require the PHY and partial MAC layers to always be powered, resulting in a standby consumption in the order of thousand fold greater.

Meeting automotive OEM standards, theQuiet-WIRE technology featured in the KSZ8061 Ethernet PHY delivers reduced EMI line emissions over unshielded twisted pair cable. Low-cost cable such as CAN or FlexRay can be deployed.

It can also be manufactured by hand with up to 5cm of untwisted section at each connector, without the need for sheathing to provide the lowest possible costs.

The reduced electrical noise provided by the PoE common mode noise rejection and isolated camera ground, can optimise camera sensor image quality.

This is in addition to the reduced thermal noise resulting from KSZ8061 low power 100BASE-TX technology. Reduced heat dissipation enhances sensor performance and translates into increased reliability and better fuel efficiencies.

Quiet-WIRE technology used in the camera solution reduces emissions and provides enhanced immunity, highlighted by bulk current injection performance. Exceeding all automotive OEM limits, the PHY receiver demonstrates error-free in the presence of 200mA noise current injection, across the complete frequency range 1MHz to 400MHz.

The enhanced PHY receiver design in the KSZ8061 provides minimum 130-meter error free cable reach, even with Quiet-WIRE emission filtering enabled. Such performance is useful for industrial and commercial vehicles, because immunity and cable reach typically is longer than the 15-meter length maximum car wiring.

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