ADN2865 Analog Devices, Inc., ADN2865 Datasheet - Page 28

• Manufacturer Part Number: ADN2865
• Description: Continuous Rate 12.3mb/s To 2.7gb/s Clock And Data Recovery Ic W/loop Timed Serdes
• Manufacturer: Analog Devices, Inc.

ADN2865
DC-COUPLED APPLICATION
The inputs to the ADN2865 can also be dc-coupled. This might
be necessary in burst mode applications, where there are long
periods of CIDs, and baseline wander cannot be tolerated. If the
inputs to the ADN2865 are dc-coupled, care must be taken not
to violate the input range and common-mode level require-
ments of the ADN2865 (see Figure through Figure ). If dc
coupling is required, and the output levels of the TIA do not
adhere to the levels shown in Figure , then level shifting and/or
an attenuator must be between the TIA outputs and the
ADN2865 inputs.
N OT ES:
1. D uring data patterns with high transition density, differential D C voltage at V1 and V2 is zero.
2. When the output of the T I A goes to CI D, V1 and V1b are driven to different D C levels. V2 and V2b discharge to the Vref level which
effectively introduces a differential D C offset across the AC coupling capacitors.
3. When the burst of data starts again, the differential D C offset across the AC coupling capacitors is applied to the input levels causing
a D C shift in the differential input. T his shift is large enough such that one of the states, either H I or L O depending on the levels of
V1 and V1b when the T IA went to CID, is cancelled out. T he quantizer will not recognize this as a valid state.
4. T he D C offset slowly discharges until the differential input voltage exceeds the sensitivity of the AD N 2817. T he quantizer will be able
to recognize both H I and L O states at this point.
V1b
Vdiff
V2b
Vdiff = V2-V2b
VT H = AD N 2817 Quantizer T hreshold
V1
V2
VCC
1
T IA
V1b
V1
C I N
2
V2b
V2
Figure 30. Example of Baseline Wander
PIN
N IN
50
50
V REF
Rev. PrA | Page 28 of 33
AD N 2817
L imamp
3
VCC
CD R
TIA
Figure 31. DC-Coupled Application
4
Preliminary Technical Data
0.1u F
C OUT
50 Ω
P I N
V R E F
N I N
DATAOU T N
DATAOU T P
A D N 2 8 65
5 0
50
3k
VT H
Vref
2.5V