AD8153 datasheet(21/24 Pages) AD

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AD8153

Rev. 0 | Page 21 of 24

OUTPUT COMPLIANCE

Figure 40 is a graphical depiction of the single-ended waveform

at the output of the AD8153. The common-mode level (VOCM)

and the amplitude (VOSE) of this waveform are a function of the

output tail current (IT), the output termination supply voltage

(VTTO), the topology of the far-end receiver, and whether ac- or

dc-coupling is used. Keep in mind that the output tail current

varies with the pre-emphasis level. The user must ensure that

the high (VH) and low (VL) voltage excursions at the output are

within the single-ended absolute voltage range limits as

specified in Table 1. Failure to understand the implications of

output signal levels and the choice of ac- or dc-coupling may

lead to transistor saturation and poor transmitter performance.

Table 9 shows an example calculation of the output levels for the

typical case, where VCC = VTTO = 3.3 V, with 50 Ω far-end

terminations to a 3.3 V supply.

VOCM

VOSE-DC VOSE-BOOST

VTTO

~320ps

Figure 40. Single-Ended Output Waveform

Table 9. Output Voltage Levels

DC-Coupled

AC-Coupled

PE Setting

IT (mA)

VOSE-DC (mV p-p)

VOSE-BOOST (mV p-p)

VOCM (V)

VH (V)

VL (V)

VOCM (V)

VH (V)

VL (V)

400

3.1

3.3

2.9

3.1

2.7

400

500

3.05

3.3

2.8

3.05

2.55

400

600

3.3

2.7

2.4

400

700

2.95

3.3

2.6

2.95

2.25

Table 10. Symbol Definitions

Symbol

Formula

Definition

VOSE-DC

Single-ended output voltage swing after settling

VOSE-BOOST

×25

Boosted single-ended output voltage swing

VOCM (dc-coupled)

−

TTO

Common-mode voltage when the output is dc-coupled

VOCM (ac-coupled)

−

TTO

Common-mode voltage when the output is ac-coupled

VOCM + VOSE-BOOST/2

High single-ended output voltage excursion

VOCM - VOSE-BOOST/2

Low single-ended output voltage excursion

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