LT1793
Low Noise,
Picoampere Bias Current,
JFET Input Op Amp
U
FEATURES
DESCRIPTIO
The LT®1793 achieves a new standard of excellence in
noiseperformanceforaJFETopamp.Forthefirsttimelow
voltage noise (6nV/√Hz) is simultaneously offered with
extremely low current noise (0.8fA/√Hz), providing the
lowest total noise for high impedance transducer applica-
tions. Unlike most JFET op amps, the very low input bias
current (3pA typ) is maintained over the entire common
moderangewhichresultsinanextremelyhighinputresis-
tance (1013Ω). When combined with a very low input ca-
pacitance (1.5pF) an extremely high input impedance
results, making the LT1793 the first choice for amplifying
low level signals from high impedance transducers. The
lowinputcapacitancealsoassureshighgainlinearitywhen
buffering AC signals from high impedance transducers.
■
Input Bias Current, Warmed Up: 10pA Max
■
100% Tested Low Voltage Noise: 8nV/√Hz Max
■
A Grade 100% Temperature Tested
■
Offset Voltage Over Temp: 1mV Max
Input Resistance: 1013Ω
■
■
Very Low Input Capacitance: 1.5pF
■
Voltage Gain: 1 Million Min
■
Gain-Bandwidth Product: 4.2MHz Typ
■
Guaranteed Specifications with ±5V Supplies
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APPLICATIO S
■
Photocurrent Amplifiers
■
Hydrophone Amplifiers
■
High Sensitivity Piezoelectric Accelerometers
TheLT1793isunconditionallystableforgainsof1ormore,
even with 1000pF capacitive loads. Other key features are
250µV VOS and a voltage gain over 4 million. Each indi-
vidual amplifier is 100% tested for voltage noise, slew rate
(3.4V/µs) and gain-bandwidth product (4.2MHz).
■
Low Voltage and Current Noise Instrumentation
Amplifier Front Ends
■
Two and Three Op Amp Instrumentation Amplifiers
■
Active Filters
, LTC and LT are registered trademarks of Linear Technology Corporation.
Specifications at ±5V supply operation are also provided.
ForanevenlowervoltagenoisepleaseseetheLT1792data
sheet.
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TYPICAL APPLICATIO
Low Noise Light Sensor with DC Servo
C1
2pF
1kHz Output Voltage Noise
Density vs Source Resistance
10k
+
V
R1
1M
–
–
+
2
3
7
V
N
1k
100
10
+
6
V
LT1793
OUT
R
SOURCE
C2 0.022µF
D2
1N914
4
–
+
V
V
R2
100k
C
D
–
D1
1N914
R3
1k
V
N
2N3904
LT1097
SOURCE
T
= 25°C
= ±15V
A
S
+
RESISTANCE
ONLY
V
HAMAMATSU
S1336-5BK
(908) 231-0960
R5
R4
10k 1k
1
100
1k 10k 100k 1M 10M
1G
100M
–
1793 TA01
V
R2C2 > C1R1
SOURCE RESISTANCE (Ω)
C
V
= PARASITIC PHOTODIODE CAPACITANCE
= 100mV/µWATT FOR 200nm WAVE LENGTH
D
OUT
2
2
–
V
N
=
√
(V
OP AMP
)
+ 4kTR + 2qI R
V
S
B
S
330mV/µWATT FOR 633nm WAVE LENGTH
1793 TA02
1