参数资料
型号: SP8026
元件分类: 光电元器件
英文描述: LINEAR OUTPUT PHOTO DETECTOR
封装: 3 X 3.50 MM, COB, 8 PIN
文件页数: 4/8页
文件大小: 93K
代理商: SP8026
4
Rev. 6/02/03
SP8024, 25, 26 200V/s Integrated APC Amplifier
Copyright 2003 Sipex Corporation
There are internal buffering resistors and a
MOSFET switch resistance in series with the
external Rgain. These internal resistances add
up to a nominal value of 62
. Therefore the true
gain equation is:
GAIN = 1 +
Rf1 + Rf2
REXT + 62
This gives a nominal external Rgain value of
324 - 62 = 262
for a gain of 6.25.
The constraints on this stage are the parasitic
capacitances associated with the input pins. The
resistors used for setting the system gain are
actually subminiature potentiometers. They are
used for calibrating out systematic variations in
the optical path.
Pins 5 and 6 connect to the summing node of the
gain stage through MOSFET switches. When a
capacitor is added to the summing node of an
inverting amplifier it creates a pole in the re-
sponse. If this pole increases enough to interfere
with the internal compensation of the amplifier,
instability occurs. This instability appears as over-
shoot in the transient response. The stray capaci-
tance at pins 5 and 6 should be kept below 1pF.
This stage also allows the part to drive high
capacitive loads. The maximum load capaci-
tance is 50pF bulk. The actual load is typically
a flexible ribbon cable (FLEX) that acts like a
transmission line. This presents a distributed
capacitive load plus inductance and resistance.
In this case care should be taken to match the
characteristic impedance of the line at the far
end to avoid standing waves and ringing. The
buffer is designed to drive 1k
to ground. How-
ever, this resistor can be adjusted in value to
accommodate the characteristic impedance of
the signal trace.
Variable Gain Amplifier: continued
Figure 1. System Gain versus Gain Set Resisitor
SP8026 Differential APC Sensitivity
versus Gain Set Resistor
6.0
5.0
4.0
3.0
2.0
1.0
0.0
-1.0
-2.0
-3.0
-4.0
-5.0
-6.0
-7.0
-8.0
-9.0
-10.0
-11.0
-12.0
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
Resistance ()
Gain
(dB)
6.0
5.7
5.3
5.0
4.7
4.3
4.0
3.7
3.3
3.0
2.7
2.3
2.0
1.7
1.3
1.0
0.7
0.3
0.0
System
Sensitivity
(mV/
W)
RGAIN
REXT
Sensitivity
THEORY OF OPERATION : Continued
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