LT1007 Datasheet, PDF (11/16 Pages) Linear Technology – Low Noise, High Speed Precision Operational Amplifiers

LT1007/LT1037
APPLICATIONS INFORMATION
The LT1007/LT1037 achieve their low noise, in part, by
operating the input stage at 120µA versus the typical 10µA
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)² + (current noise • R_S)² +
(resistor noise)²]^1/2
Three regions can be identified as a function of source
resistance:
(i) R_S ≤ 400Ω. Voltage noise dominates
} (ii) 400Ω ≤ RS ≤ 50k at 1kHz Resistor noise
400Ω ≤ R_S ≤ 8k at 10Hz ^dominates
} (iii) RS > 50k at 1kHz Current noise
R_S > 8k at 10Hz ^dominates
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.
TYPICAL APPLICATIONS
Gain 1000 Amplifier with 0.01% Accuracy, DC to 5Hz
340k 15k 20k
1% 5% TRIM
365Ω
1%
15V
2– 7
LT1037
3+
4
6
OUTPUT
RN60C FILM RESISTORS
INPUT
–15V
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 Error vs Frequency
Closed-Loop Gain = 1000
1
TYPICAL
PRECISION
OP AMP
0.1
LT1007
LT1037
0.01
0.001
0.1
GAIN ERROR = ^{CLOSED-LOOP GAIN}
OPEN-LOOP GAIN
1
10
100
FREQUENCY (Hz)
1007/37 TA03
11