GTD-18464 Rev.2.0
1
Semiconductor
KGA4140
BLOCK DIAGRAM AND APPLICATION OUTLINES
Vd
Vd
0.1µF
220pF
0.1µF
220pF
V(PD)
Photo
KGA4140
D iode
Vd1
Vd2
Vd3
OUT
____
OUT
Blocking
Capacitor
IN
Output Offset
Adjustment Circuit
15pF
20kohm
20kohm
15pF
GND1
Cap1
220pF
0.1µF
Cap2
G N D 2 GND3
220pF
0.1µF
Vd
R1
-
OP Amp.
+
V th
Vz = 2.6 - 3.0V
R2
R1:R2 = 1:3
External Capacitors of Cap1 and Cap2 pads
The low frequency cutoff of KGA4140 can be reduced by adding external capacitors to “Cap1” and
“Cap2” pads, respectively. KGA4140 has on-chip 20kΩ resistors with shunt 15pF capacitors to ground.
Without the external capacitors, the low frequency cutoff will be 30MHz.
The low frequency cutoff with the external capacitors is almost given by
1
f
low
−
cutoff
≈
×
(10 ~ 100)
R
=
20
k
Ω
2
π
⋅
R
⋅
C
ext
External Components and Adjustable Decision Threshold
The “output offset adjustment amplifier” feeds back a DC offset from the output to the input of “limiting
amplifier” stage, to eliminate the offset of KGA4140 outputs, for small signal input. To control the DC
offset between the two outputs for large signal operation, the use of the external components, shown in
the diagram above, is recommended. Under the configuration as in the diagram, there are typical
relationship between the voltages of “Cap1” and “Cap2” (Vcap1 and Vcap2) and the input current, as
following.
5/8
OKI [ OKI ELECTRONIC COMPONETS ]
