AD8155ACPZ-R7 datasheet(23/35 Pages) AD

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Data Sheet

AD8155

Rev. A | Page 23 of 35

Power Saving Considerations

Whereas the AD8155 power consumption is very low

compared to similar devices, careful control of its operating

conditions can yield further power savings. Significant power

reduction can be realized by operating the part at a lower voltage.

Compared to 3.3 V operation, a supply voltage of 1.8 V can

result in power savings of ~45%. There is no performance

penalty when operating at lower voltage. An initialization

sequence is required to enable the AD8155 in a low power

mode (see the Applications Information section).

A second measure is to disable transmitters when they are not

being used. This can be done on a static basis if the output is

not used or on a dynamic basis if the output does not have a

constant stream of traffic. On transmit disable (Register 0x48,

switch currents are disabled. The LOS-activated squelch disables

only the output switch current, ITOT. Superior power saving is

achieved by using the TX and RX disable registers to turn off an

unused lane as opposed to relying on the AD8155 transmit

squelch feature.

Because the majority of the power dissipated is in the output stage,

some of its flexibility can be used to lower the power consumption.

First, the output current and output preemphasis settings can

be programmed to the smallest amount required to maintain

BER performance. If an output circuit always has a short length

and the receiver has good sensitivity, then a lower output

current can be used.

It is also possible to lower the voltage on VTTO to lower the

power dissipation. The amount that VTTO can be lowered is

dependent on the lowest of all the output’s VOL and VCC. This

is determined by the output that is operating at the highest

programmed output current. Table 1 and Table 19 list

minimum output levels.

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