December 2001
LF155/LF156/LF256/LF257/LF355/LF356/LF357
JFET Input Operational Amplifiers
n Logarithmic amplifiers
n Photocell amplifiers
These are the first monolithic JFET input operational ampli-
n Sample and Hold circuits
General Description
fiers to incorporate well matched, high voltage JFETs on the
Common Features
™
same chip with standard bipolar transistors (BI-FET Tech-
nology). These amplifiers feature low input bias and offset
currents/low offset voltage and offset voltage drift, coupled
with offset adjust which does not degrade drift or
common-mode rejection. The devices are also designed for
high slew rate, wide bandwidth, extremely fast settling time,
low voltage and current noise and a low 1/f noise corner.
n Low input bias current: 30pA
n Low Input Offset Current: 3pA
n High input impedance: 1012Ω
n Low input noise current:
n High common-mode rejection ratio: 100 dB
n Large dc voltage gain: 106 dB
Features
Advantages
Uncommon Features
n Replace expensive hybrid and module FET op amps
n Rugged JFETs allow blow-out free handling compared
with MOSFET input devices
n Excellent for low noise applications using either high or
low source impedance—very low 1/f corner
n Offset adjust does not degrade drift or common-mode
rejection as in most monolithic amplifiers
n New output stage allows use of large capacitive loads
(5,000 pF) without stability problems
LF155/ LF156/ LF257/
Units
LF355
LF256/
LF356
1.5
LF357
(AV=5)
1.5
j
Extremely
fast settling
time to
4
µs
0.01%
j
j
j
Fast slew
rate
5
12
5
50
20
12
V/µs
MHz
n Internal compensation and large differential input voltage
capability
Wide gain
bandwidth
Low input
noise
2.5
20
Applications
n Precision high speed integrators
n Fast D/A and A/D converters
n High impedance buffers
12
voltage
n Wideband, low noise, low drift amplifiers
Simplified Schematic
00564601
*
3pF in LF357 series.
™
™
BI-FET , BI-FET II are trademarks of National Semiconductor Corporation.
© 2001 National Semiconductor Corporation
DS005646
www.national.com