LT1028_01 Datasheet, PDF (12/20 Pages) Linear Technology – Ultralow Noise Precision High Speed Op Amps

LT1028/LT1128
U
APPLICATI S I FOR ATIO – OISE
Noise Testing – Current Noise
Current noise density (I_n) is defined by the following
formula, and can be measured in the circuit shown:
I_n =
[e_no² – (31 × 18.4nV/√Hz)²]^1/2
20k × 31
1.8k
10k
60Ω _10k
–
LT1028
LT1128
+
e_no
1028/1128 AI04
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.
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.
Automated Tester Noise Filter
10
0
–10
–20
CURRENT VOLTAGE
NOISE NOISE
–30
–40
–50
100
1k
10k
100k
FREQUENCY (Hz)
LT1028/1128 • AI05
APPLICATI S 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
1k
1
2_– 8
INPUT
3
LT1028
LT1128
+₄
76
15V
OUTPUT
–15V
1028/1128 AI06
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
12