Datasheet

11
LT1792
U
SA
O
PP
L
IC
AT
ITY
P
I
CA
L
Low Noise Light Sensor with DC Servo
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
7
V
+
V
–
4
1792 TA05
R1
1M
C1
2pF
6
3
2
–
+
LT1792
R2C2 > C1R1
C
D
= PARASITIC PHOTODIODE CAPACITANCE
V
O
= 100mV/
µ
WATT FOR 200nm WAVE LENGTH
330mV/
µ
WATT FOR 633nm WAVE LENGTH
R5
1k
D2
1N914
2N3904
V
–
R4
1k
D1
1N914
R3
1k
6
3
2
–
+
LT1792
C2
0.022
µ
F
HAMAMATSU
S1336-5BK
OUTPUT
R2
100k
C
D
1. ASSUME VOLTAGE NOISE OF LT1792 AND 51Ω SOURCE RESISTOR = 4.3nV/√Hz
2. GAIN WITH n LT1792s IN PARALLEL = n × 200
3. OUTPUT NOISE = √n × 200 × 4.3nV/√Hz
4. INPUT REFERRED NOISE =
OUTPUT NOISE
=
4.3
nV/√Hz
n × 200
√
n
5. NOISE CURRENT AT INPUT INCREASES
√
n TIMES
7
15V
–15V
4
7
15V
–15V
4
1k
1792 TA04
6
2
3
1k
1k
6
2
3
–
+
A2
LT1792
–
+
1k
51Ω
51Ω
51Ω
6
2
3
An
LT1792
10k
6
3
2
–
+
LT1792
–
+
A1
LT1792
1k
1k
OUTPUT
Paralleling Amplifiers to Reduce Voltage Noise