AD8015
AC COUPLED PHOTODIODE APPLICATION FOR
IMPROVED DYNAMIC RANGE
and typical sensitivity of –35 dBm. AC coupling the input also
results in improved pulse width modulation performance.
Careful attention to minimize parasitic capacitance at the
AD8015 input (from the photodetector input), R
AC
and C
AC
are
critical for sensitivity performance in this application. Note that
C
AC
of 0.01
µF
was chosen for a low frequency cutoff equal to
2.2 kHz.
+V
S
AC coupling the photodiode current input to the AD8015 (Fig-
ure 17) extends fiber optic receiver overload by 3 dB while sacri-
ficing only 1 dB of sensitivity (increasing receiver dynamic range
by 2 dB). This application results in typical overload of –4 dBm,
+V
S
AD8015
1
10kΩ
8
50Ω
2
+1
G = 30
3
G=3
50Ω
+1
4
– +
1.7V
C1
+V
S
5
6
7
LPF:
R
3dB@
0.7 x F
LPF:
3dB@
0.7 x F
V1
R
CLOCK
RECOVERY
QUANTIZER
R > 40Ω
C1 >100pF
4.5V < V
S
< 11V
CLK
DATA
C
AC
R
AC
7k
0.01µF
Figure 17. AC Coupled Photodiode Application for Improved Dynamic Range
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
8-Lead Small Outline IC Package (SO-8)
0.1968 (5.00)
0.1890 (4.80)
8
1
5
4
0.1574 (4.00)
0.1497 (3.80)
0.2440 (6.20)
0.2284 (5.80)
PIN 1
0.0098 (0.25)
0.0040 (0.10)
0.0688 (1.75)
0.0532 (1.35)
0.0196 (0.50)
0.0099 (0.25)
x 45°
0.0500 0.020 (0.51)
SEATING
(1.27) 0.013 (0.33)
PLANE
BSC
0.0098 (0.25)
0.0075 (0.19)
8°
0° 0.0500 (1.27)
0.0160 (0.41)
–8–
REV. A
PRINTED IN U.S.A.
C1973–6–1/96
AD [ ANALOG DEVICES ]
