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LT1007CN8

Low Noise, High Speed Precision Operational Amplifiers

Linear Technology 

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 • RS)2 +

(resistor noise)2]1/2

Three regions can be identified as a function of source

resistance:

(i) RS ≤ 400Ω. Voltage noise dominates

} (ii) 400Ω ≤ RS ≤ 50k at 1kHz Resistor noise

400Ω ≤ RS ≤ 8k at 10Hz dominates

} (iii) RS > 50k at 1kHz Current noise

RS > 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

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