Datasheet

AD8158

Rev. B | Page 24 of 36

Power Saving Considerations

Whereas the AD8158 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 oper-

ting at lower voltage.

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, I

TTO

. 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 AD8158

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 V

TTO

to lower the

power dissipation. The amount that V

TTO

can be lowered is

dependent on the lowest of all the output’s V

and V

. This

is determined by the output that is operating at the highest

programmed output current. Table 1 and Table 19 list minimum

output levels.