10
LT1007/LT1037
sn100737 100737fbs
APPLICATIONS INFORMATION
WU
U
As with all operational amplifiers when RF > 2k, a pole will
be created with RF and the amplifier’s input capacitance,
creating additional phase shift and reducing the phase
margin. A small capacitor (20pF to 50pF) in parallel with RF
will eliminate this problem.
Noise Testing
The 0.1Hz to 10Hz peak-to-peak noise of the LT1007/
LT1037 is measured in the test circuit shown (Figure 5a).
The frequency response of this noise tester (Figure 5b)
indicates that the 0.1Hz corner is defined by only one zero.
The test time to measure 0.1Hz to 10Hz noise should not
exceed ten seconds, as this time limit acts as an additional
zero to eliminate noise contributions from the frequency
band below 0.1Hz.
Measuring the typical 60nV peak-to-peak noise perfor-
mance of the LT1007/LT1037 requires special test
precautions:
1. The device should be warmed up for at least five
minutes. As the op amp warms up, its offset voltage
changes typically 3
V due to its chip temperature
increasing 10
°C to 20°C from the moment the power
supplies are turned on. In the ten-second measurement
interval these temperature-induced effects can easily
exceed tens of nanovolts.
2. For similar reasons, the device must be well shielded
from air currents to eliminate the possibility of thermo-
electric effects in excess of a few nanovolts, which
would invalidate the measurements.
3. Sudden motion in the vicinity of the device can also
“feedthrough” to increase the observed noise.
A noise voltage density test is recommended when mea-
suring noise on a large number of units. A 10Hz noise
voltage density measurement will correlate well with a
0.1Hz to 10Hz peak-to-peak noise reading since both
results are determined by the white noise and the location
of the 1/f corner frequency.
Current noise is measured in the circuit shown in Figure 6
and calculated by the following formula:
i
e
nV
M
n
no
=
() ()
()( )
2
12
130
101
1
101
/
FREQUENCY (Hz)
100
90
80
70
60
50
40
30
0.01
1
10
100
1007/37F05b
0.1
GAIN
(dB)
1007/37 F05a
10
0.1
F
4.7
F
VOLTAGE GAIN
= 50,000
24.3k
100k
–
+
–
+
*
LT1007
LT1037
LT1001
2k
4.3k
110k
100k
SCOPE
× 1
RIN = 1M
*DEVICE UNDER TEST
NOTE: ALL CAPACITOR VALUES ARE FOR
NONPOLARIZED CAPACITORS ONLY
2.2
F
0.1
F
22
F
Figure 5a. 0.1Hz to 10Hz Noise Test Circuit
1007/37 F06
100
100k
–
+
LT1007
LT1037
500k
eno
Figure 6
Figure 5b. 0.1Hz to 10Hz Peak-to-
Peak Noise Tester Frequency
Response