LT1037 Linear Technology Corporation, LT1037 Datasheet - Page 11

• Manufacturer Part Number: LT1037
• Description: Low Noise, High Speed Precision Operational Amplifiers
• Manufacturer: Linear Technology Corporation

APPLICATIONS
The LT1007/LT1037 achieve their low noise, in part, by
operating the input stage at 120 A versus the typical 10 A
of most other op amps. Voltage noise is inversely propor-
tional while current noise is directly proportional to the
square root of the input stage current. Therefore, the
LT1007/LT1037’s current noise will be relatively high. At
low frequencies, the low 1/f current noise corner fre-
quency ( 120Hz) minimizes current noise to some extent.
In most practical applications, however, current noise will
not limit system performance. This is illustrated in the
Total Noise vs Source Resistance plot in the Typical
Performance Characteristics section, where:
Total Noise = [(voltage noise)
(resistor noise)
TYPICAL APPLICATIONS
THE HIGH GAIN AND WIDE BANDWIDTH OF THE LT1037 (AND LT1007) IS
USEFUL IN LOW FREQUENCY, HIGH CLOSED-LOOP GAIN AMPLIFIER
APPLICATIONS. A TYPICAL PRECISION OP AMP MAY HAVE AN OPEN-LOOP
GAIN OF ONE MILLION WITH 500kHz BANDWIDTH. AS THE GAIN ERROR
PLOT SHOWS, THIS DEVICE IS CAPABLE OF 0.1% AMPLIFYING ACCURACY
UP TO 0.3Hz ONLY. EVEN INSTRUMENTATION RANGE SIGNALS CAN VARY
AT A FASTER RATE. THE LT1037’S “GAIN PRECISION-BANDWIDTH
PRODUCT” IS 200 TIMES HIGHER AS SHOWN.
Gain 1000 Amplifier with 0.01% Accuracy, DC to 5Hz
2
]
365
1/2
1%
U
INPUT
340k
1%
3
2
INFORMATION
U
–
+
LT1037
–15V
15k
5%
15V
2
+ (current noise • R
7
4
U
TRIM
20k
W
RN60C FILM RESISTORS
6
OUTPUT
U
S
)
2
+
Three regions can be identified as a function of source
resistance:
(i) R
(ii) 400
(iii) R
Clearly the LT1007/LT1037 should not be used in region
(iii), where total system noise is at least six times higher
than the voltage noise of the op amp, i.e., the low voltage
noise specification is completely wasted.
400
R
S
S
S
0.001
0.01
0.1
> 50k at 1kHz
> 8k at 10Hz
1
0.1
400 . Voltage noise dominates
PRECISION
R
R
Closed-Loop Gain = 1000
TYPICAL
Gain Error vs Frequency
S
S
OP AMP
GAIN ERROR =
50k at 1kHz
8k at 10Hz
FREQUENCY (Hz)
1
}
LT1007
Current noise
dominates
CLOSED-LOOP GAIN
OPEN-LOOP GAIN
10
LT1007/LT1037
}
LT1037
Resistor noise
dominates
1007/37 TA03
100
sn100737 100737fbs
11