Data Sheet ADN2815
Rev. C | Page 21 of 24
04952-0-027
50
50
PIN
V
REF
NIN
C
IN
C
OUT
C
OUT
V1
C
IN
V1b
V2
V2b
TIA BUFFER
CDR
+
–
VCC
DATAOUTP
DATAOUTN
1
V1
V1b
V2
V2b
DIFF
234
VREF
VTH
ADN2815
V
DIFF
= V2–V2b
VTH = ADN2815 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 ADN2815. THE
QUANTIZER CAN RECOGNIZE BOTH HIGH AND LOW STATES AT THIS POINT.
Figure 21. Example of Baseline Wander
