Datasheet
Data Sheet ADN2814
Rev. C | Page 23 of 28
50Ω
50Ω
PIN
V
REF
NIN
C
IN
C
OUT
C
OUT
V1
C
IN
V1b
V2
V2b
TIA LIMAMP
CDR
+
–
VCC
DATAOUTP
DATAOUTN
1
V1
V1b
V2
V2b
V
DIFF
234
VREF
VTH
ADN2814
V
DIFF
= V2–V2b
VTH = ADN2813 QUANTIZER THRESHOLD
NOTES:
1. DURING DATA PATTERNS WITH HIGH TRANSITION DENSITY, DIFFERENTIAL DC VOLTAGE AT V1 AND V2 IS ZERO.
2. WHEN THE OUTPUT OF THE TIA GOES TO CID, V1 AND V1b ARE DRIVEN TO DIFFERENT DC LEVELS. V2 AND V2b DISCHARGE TO THE
VREF LEVEL, WHICH EFFECTIVELY INTRODUCES A DIFFERENTIAL DC OFFSET ACROSS THE AC COUPLING CAPACITORS.
3. WHEN THE BURST OF DATA STARTS AGAIN, THE DIFFERENTIAL DC OFFSET ACROSS THE AC COUPLING CAPACITORS IS APPLIED TO
THE INPUT LEVELS CAUSING A DC SHIFT IN THE DIFFERENTIAL INPUT. THIS SHIFT IS LARGE ENOUGH SUCH THAT ONE OF THE STATES,
EITHER HIGH OR LOW DEPENDING ON THE LEVELS OF V1 AND V1b WHEN THE TIA WENT TO CID, IS CANCELED OUT. THE QUANTIZER
DOES NOT RECOGNIZE THIS AS A VALID STATE.
4. THE DC OFFSET SLOWLY DISCHARGES UNTIL THE DIFFERENTIAL INPUT VOLTAGE EXCEEDS THE SENSITIVITY OF THE ADN2814. THE
QUANTIZER CAN RECOGNIZE BOTH HIGH AND LOW STATES AT THIS POINT.
04949-027
Figure 26. Example of Baseline Wander
DC-COUPLED APPLICATION
The inputs to the ADN2814 can also be dc-coupled. This may
be necessary in burst mode applications, where there are long
periods of CIDs, and baseline wander cannot be tolerated. If the
inputs to the ADN2814 are dc-coupled, care must be taken not
to violate the input range and common-mode level require-
ments of the ADN2814 (see Figure 27 through Figure 29). If dc
coupling is required, and the output levels of the TIA do not
adhere to the levels shown in Figure 28, then level shifting
and/or an attenuator must be between the TIA outputs and the
ADN2814 inputs.
50Ω
0.1μF
50Ω
3kΩ
NIN
PIN
ADN2814
2.5V
VREF
50Ω
50Ω
TIA
VCC
04949-028
Figure 27. DC-Coupled Application
PIN
INPUT (V)
V p-p = PIN – NIN = 2
×
V
SE
= 10mV AT SENSITIVITY
V
SE
= 5mV MIN
V
CM
= 2.3V MIN
(DC-COUPLED)
NIN
04949-029
Figure 28. Minimum Allowed DC-Coupled Input Levels
PIN
INPUT (V)
V p-p = PIN – NIN = 2
×
V
SE
= 2.0V MAX
V
SE
= 1.0V MAX
V
CM
= 2.3V
(DC-COUPLED)
NIN
04949-030
Figure 29. Maximum Allowed DC-Coupled Input Levels