AD8159(RevC) データシートの表示（PDF） - Analog Devices
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AD8159 Datasheet PDF : 21 Pages
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AD8159
Data Sheet
Consider the following example: a driver dc-coupled to the
input of the AD8159. The AD8159 input termination voltage
(VTTI) and the driver output termination voltage (VTTOD) are both
set to the same level; that is, VTTI = VTTOD = 3.3 V. If an 800 mV p-p
differential swing is desired, the total output current of the driver
is 16 mA. At balance, the output current is divided evenly between
the two sides of the differential signal path, 8 mA to each side.
This 8 mA of current flows through the parallel combination of the
55 Ω input termination resistor on the AD8159 and the 50 Ω
output termination resistor on the driver, resulting in a common-
mode level of
VTTI − 8 mA × (50 Ω || 55 Ω) = VTTI − 210 mV
The user can then use Figure 25 to determine the allowable
range of values for VTTI that meets the input compliance range
based on an 800 mV p-p differential swing.
OUTPUT COMPLIANCE
Figure 43 is depicts the single-ended waveform at the output of
the AD8159. The common-mode level (VOCM) and the amplitude
(VOSE-BOOST) 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 coupling 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 coupling or dc coupling may lead to transistor
saturation and poor transmitter performance.
Table 9 and Table 10 show the typical output levels for Port A/
Port B and Port C, respectively, where VCC = VTTO = 3.3 V, with
50 Ω far-end terminations to a 3.3 V supply.
VTTO
VH
VOCM
VOSE-DC VOSE-BOOST
VL
~320ps
Figure 43. Single-Ended Output Waveform
Table 9. Output Voltage Levels for Port A and Port B
PE Setting
0
1
2
3
IT (mA)
16
20
24
28
VOSE-DC (mV p-p)
400
400
400
400
VOSE-BOOST (mV p-p)
400
500
600
700
DC-Coupled
VOCM (V) VH (V) VL (V)
3.1
3.3
2.9
3.05
3.3
2.8
3
3.3
2.7
2.95
3.3
2.6
AC-Coupled
VOCM (V) VH (V) VL (V)
2.9
3.1
2.7
2.8
3.05 2.55
2.7
3
2.4
2.6
2.95 2.25
Table 10. Output Voltage Levels for Port C
PE Setting
0
1
2
3
IT (mA)
20
24
28
32
VOSE-DC (mV p-p)
400
400
400
400
VOSE-BOOST (mV p-p)
400
500
600
700
DC-Coupled
VOCM (V) VH (V) VL (V)
3.05
3.25 2.85
3
3.25 2.75
2.95
3.25 2.65
2.9
3.25 2.55
AC-Coupled
VOCM (V) VH (V) VL (V)
2.8
3
2.6
2.7
2.95 2.45
2.6
2.9
2.3
2.5
2.85 2.15
Table 11. Symbol Definitions
Symbol
VOSE-DC
VOSE-BOOST
VOCM (dc-coupled)
VOCM (ac-coupled)
VH
VL
Formula
IT PE = 0 × 25 Ω
IT × 25 Ω
VTTO – IT/2 × 25 Ω
VTTO – IT/2 × 50 Ω
VOCM + VOSE-BOOST/2
VOCM − VOSE-BOOST/2
Definition
Single-ended output voltage swing after settling
Boosted single-ended output voltage swing
Common-mode voltage when the output is dc-coupled
Common-mode voltage when the output is ac-coupled
High single-ended output voltage excursion
Low single-ended output voltage excursion
Rev. C | Page 20 of 21
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