OPT101_03 BURR-BROWN [Burr-Brown Corporation], OPT101_03 Datasheet - Page 10

• Manufacturer Part Number: OPT101_03
• Description: MONOLITHIC PHOTODIODE AND SINGLE-SUPPLY TRANSIMPEDANCE AMPLIFIER
• Manufacturer: BURR-BROWN [Burr-Brown Corporation]

Applications using a feedback resistor significantly larger than
the internal 1M
Input bias current of the op amp and dark current of the
photodiode increase significantly at higher temperatures. This
increase combined with the higher gain (R
the op amp output to be driven to ground at high temperatures.
Such applications may require a positive bias voltage applied to
pin 8 to ensure that the op amp output remains in the linear
operating region when the photodiode is not exposed to light.
Alternatively, a dual power supply can be used. The output may
be negative when sensing dark conditions.
LIGHT SOURCE POSITIONING
The OPT101 is tested with a light source that uniformly
illuminates the full area of the integrated circuit, including
the op amp. Although IC amplifiers are light-sensitive to
some degree, the OPT101 op amp circuitry is designed to
minimize this effect. Sensitive junctions are shielded with
metal, and the photodiode area is very large relative to the op
amp input circuitry.
If your light source is focused to a small area, be sure that it
is properly aimed to fall on the photodiode. A narrowly
focused beam falling on only the photodiode will provide
improved settling times compared to a source that uniformly
illuminates the full area of the die. If a narrowly focused light
source were to miss the photodiode area and fall only on the
op amp circuitry, the OPT101 would not perform properly.
The large 0.09" x 0.09" (2.29mm x 2.29mm) photodiode area
allows easy positioning of narrowly focused light sources.
The photodiode area is easily visible, as it appears very dark
compared to the surrounding active circuitry.
The incident angle of the light source also effects the apparent
sensitivity in uniform irradiance. For small incident angles, the
loss in sensitivity is simply due to the smaller effective light
gathering area of the photodiode (proportional to the cosine of
the angle). At a greater incident angle, light is diffracted and
scattered by the package. These effects are shown in the typical
performance curve “Responsivity vs Incident Angle.”
FIGURE 5. Three-Wire Remote Light Measurement.
10
resistor may require special consideration.
0.01 to
0.1 F
F
> 1M ) can cause
2
8
V
B
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1M
1
3
OPT101
3pF
8pF
DYNAMIC RESPONSE
Using the internal 1M
the photodiode/op amp combination can be modeled as a
simple R • C circuit with a –3dB cutoff frequency of
approximately 14kHz. The R and C values are 1M
11pF respectively. By using external resistors, with less than
3pF parasitic capacitance, the frequency response can be
improved. An external 1M resistor used in the configuration
shown in Figure 4b will create a 23kHz bandwidth with the
same 10
of approximately 15 s (10% to 90%). Dynamic response is
not limited by op amp slew rate. This is demonstrated by the
dynamic response oscilloscope photographs showing virtually
identical large-signal and small-signal response.
Dynamic response will vary with feedback resistor value as
shown in the typical performance curve “Responsivity vs
Frequency.” Rise time (10% to 90%) will vary according to
the –3dB bandwidth produced by a given feedback resistor
value:
where:
LINEARITY PERFORMANCE
The photodiode is operated in the photoconductive mode so
the current output of the photodiode is very linear with
radiant power throughout a wide range. Nonlinearity remains
below approximately 0.05% up to 100 A photodiode current.
The photodiode can produce output currents of 1mA or
greater with high radiant power, but nonlinearity increases
to several percent in this region.
This very linear performance at high radiant power assumes
that the full photodiode area is uniformly illuminated. If the
light source is focused to a small area of the photodiode,
nonlinearity will occur at lower radiant power.
t
f
4
5
r
C
is the rise time (10% to 90%)
is the –3dB bandwidth
6
V/A dc transimpedance gain. This yields a rise time
resistor, the dynamic response of
t
r
0.35
+2.7 to
f
+36V
C
V
OUT
OPT101
SBBS002A
and