LT1007_1 Datasheet, PDF (10/16 Pages) Linear Technology – Low Noise, High Speed Precision Operational Amplifiers

LT1007/LT1037
APPLICATIONS INFORMATION
As with all operational amplifiers when R_F > 2k, a pole will
be created with R_F and the amplifier’s input capacitance,
creating additional phase shift and reducing the phase
margin. A small capacitor (20pF to 50pF) in parallel with R_F
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 3µV 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:
( ) ( ) ^{ 2}
2 ^{1/ 2}
 ^e_no ^{− 130nV • 101} 
i_n = ^

(^1MΩ)(¹⁰¹)
100Ω
100k
500k _–
LT1007
500k ₊^LT1037
Figure 6
e_no
1007/37 F06
0.1µF
100k
10Ω
–
*
LT1007
+^LT1037
VOLTAGE GAIN
= 50,000
2k
+
4.3k
4.7µF
LT1001
–
100k
*DEVICE UNDER TEST
NOTE: ALL CAPACITOR VALUES ARE FOR
NONPOLARIZED CAPACITORS ONLY
24.3k
0.1µF
Figure 5a. 0.1Hz to 10Hz Noise Test Circuit
10
22µF
2.2µF
110k
SCOPE
×1
R_IN = 1M
1007/37 F05a
100
90
80
70
60
50
40
30
0.01
0.1
1
10
100
FREQUENCY (Hz)
1007/37F05b
Figure 5b. 0.1Hz to 10Hz Peak-to-
Peak Noise Tester Frequency
Response
sn100737 100737fbs