Datasheet

AD8122 Data Sheet

Rev. 0 | Page 16 of 20

When using a single 5 V supply on the driver side, the common-

mode voltage at the driver output is typically 2.5 V (in the case

of the AD8142 driver, the common-mode voltage at the output

is fixed at 1.5 V). The largest received differential video signal is

approximately 700 mV p-p, which adds 175 mV

PEAK

to each single-

ended side of the differential signal and results in a worst-case

peak voltage of 2.675 V or 1.675 V on an AD8122 single-ended

input (assuming that there is no ground shift between the driver

and receiver). Because these levels are within the AD8122 input

voltage swing limits, such a system works well as long as the

difference in ground potential between the driver and receiver

does not cause the input voltage swing to exceed these limits.

When used, common-mode sync signals are generally applied

with a peak deviation of 500 mV during the blanking intervals

(video signal = 0 V), increasing the common-mode level from

2.5 V to 3.0 V (1.5 V to 2.0 V in the case of the AD8142 driver).

These common-mode levels are below the upper input voltage

swing limit of 4 V and, therefore, leave a margin of 1 V or 2 V

for ground shifts between the driver and receiver. To increase

the common-mode range of the overall system, use one or both

of these techniques:

• Power the driver from dual supplies (output common-mode

voltage = 0 V).

• Place an AD8143 in front of the AD8122, as shown in

Figure 31.

These techniques can be combined or applied separately.

POWER-DOWN

The power-down feature can be used to reduce power consump-

tion when a particular device is not in use. When asserted, the

pin does not place the output in a high-Z state. The input

logic levels and supply current in power-down mode are listed

in Table 1.