Datasheet

12
LT1028/LT1128
Noise Testing – Current Noise
Current noise density (I
n
) is defined by the following
formula, and can be measured in the circuit shown:
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 approxi-
mate 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.
U
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I FOR ATIO
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.
I
n
=
[e
no
2
– (31 × 18.4nV/√Hz)
2
]
1/2
20k × 31
–
+
e
no
1.8k
60Ω
LT1028
LT1128
10k
10k
1028/1128 AI04
– OISE
U
FREQUENCY (Hz)
100
–50
NOISE FILTER LOSS (dB)
–10
0
10
1k 10k 100k
LT1028/1128 • AI05
–20
–40
–30
CURRENT
NOISE
VOLTAGE
NOISE
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I FOR ATIO
General
The LT1028/LT1128 series devices may be inserted di-
rectly into OP-07, OP-27, OP-37, LT1007 and LT1037
sockets with or without removal of external nulling com-
ponents. In addition, the LT1028/LT1128 may be fitted to
5534 sockets with the removal of external compensation
components.
Offset Voltage Adjustment
The input offset voltage of the LT1028/LT1128 and its drift
with temperature, are permanently trimmed at wafer test-
ing to a low level. However, if further adjustment of V
OS
is
necessary, the use of a 1k nulling potentiometer will not
degrade drift with temperature. Trimming to a value other
Automated Tester Noise Filter
–
+
6
1k
INPUT
LT1028
LT1128
1028/1128 AI06
7
8
1
2
3
4
OUTPUT
–15V
15V
than zero creates a drift of (V
OS
/300)µV/°C, e.g., if V
OS
is
adjusted to 300µV, the change in drift will be 1µV/°C.
The adjustment range with a 1k pot is approximately
±1.1mV.
Offset Voltage and Drift
Thermocouple effects, caused by temperature gradients
across dissimilar metals at the contacts to the input