Datasheet

LT1028/LT1128
13
1028fb
applicaTions inForMaTion – noise
Noise Testing – Current Noise
Current noise density (I
n
) is defined by the following for-
mula, and can be measured in the circuit shown in Figure 4.
l
n
=
e
no
2
− 31• 18.4nV/ Hz
( )
2
⎡
⎣
⎢
⎤
⎦
⎥
20k • 31
1/2
If the Quan Tech Model 5173 is used, the noise reading is
input-referred, therefore the result should not be divided
by 31; the resistor noise should not be multiplied by 31.
100% Noise Testing
The 1kHz voltage and current noise is 100% tested on
the LT1028/LT1128 as part of automated testing; the
approximate frequency response of the filters is shown.
The limits on the automated testing are established by
extensive correlation tests on units measured with the
Quan Tech Model 5173.
10Hz voltage noise density is sample tested on every lot.
Devices 100% tested at 10Hz are available on request for
an additional charge.
10Hz current noise is not tested on every lot but it can be
inferred from 100% testing at 1kHz. A look at the current
noise spectrum plot will substantiate this statement. The
only way 10Hz current noise can exceed the guaranteed
limits is if its 1/f corner is higher than 800Hz and/or its
white noise is high. If that is the case then the 1kHz test
will fail.
Figure 5. Automated Tester Noise Filter
–
+
e
no
1.8k
60Ω
LT1028
LT1128
10k
10k
1028 F04
FREQUENCY (Hz)
100
–50
NOISE FILTER LOSS (dB)
–10
0
10
1k 10k 100k
1028 F05
–20
–40
–30
CURRENT
NOISE
VOLTAGE
NOISE
Figure 4