12

LT1028/LT1128

Noise Testing – Current Noise

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.

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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.

20k

× 31

–

+

1.8k

60

Ω

LT1028

LT1128

10k

10k

1028/1128 AI04

– OISE

FREQUENCY (Hz)

100

–50

–10

0

10

1k

10k

100k

LT1028/1128 • AI05

–20

–40

–30

CURRENT

NOISE

VOLTAGE

NOISE

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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-

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

adjusted to 300

µV, 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