10

LT1007/LT1037

sn100737 100737fbs

creating additional phase shift and reducing the phase

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

µV 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

2

12

130

101

1

101

•

/

Ω

FREQUENCY (Hz)

100

90

80

70

60

50

40

30

0.01

1

10

100

1007/37F05b

0.1

1007/37 F05a

10

Ω

0.1

µF

4.7

µF

VOLTAGE GAIN

= 50,000

24.3k

100k

–

+

*

LT1007

LT1037

LT1001

2k

4.3k

110k

100k

SCOPE

× 1

*DEVICE UNDER TEST

NOTE: ALL CAPACITOR VALUES ARE FOR

NONPOLARIZED CAPACITORS ONLY

2.2

µF

0.1

µF

22

µF

Figure 5a. 0.1Hz to 10Hz Noise Test Circuit

1007/37 F06

100

Ω

100k

LT1007

LT1037

500k

500k

Figure 6

Figure 5b. 0.1Hz to 10Hz Peak-to-

Peak Noise Tester Frequency

Response