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Low Noise, Low Drift FET Op Amp AD645

FEATURES Improved Replacement for Burr-Brown OPA-111 and OPA-121 Op Amp LOW NOISE 2 ␮V p max, 0.1 Hz to 10 Hz 10 nV/√Hz max at 10 kHz 11 fA p Current Noise 0.1 Hz to 10 Hz

CONNECTION DIAGRAMS TO-99 (H) Package

8-Pin Plastic Mini-DIP (N) Package

CASE

ED

V O T PR IF M DR I

HIGH DC ACCURACY 250 ␮V max Offset Voltage 1 ␮V/؇C max Drift 1.5 pA max Input Bias Current 114 dB Open-Loop Gain Available in Plastic Mini-DIP, 8-Pin Header Packages, or Chip Form APPLICATIONS Low Noise Photodiode Preamps CT Scanners Precision I-V Converters

PRODUCT DESCRIPTION

The AD645 is a low noise, precision FET input op amp. It offers the pico amp level input currents of a FET input device coupled with offset drift and input voltage noise comparable to a high performance bipolar input amplifier. The AD645 has been improved to offer the lowest offset drift in a FET op amp, 1 µV/°C. Offset voltage drift is measured and trimmed at wafer level for the lowest cost possible. An inherently low noise architecture and advanced manufacturing techniques result in a device with a guaranteed low input voltage noise of 2 µV p, 0.1 Hz to 10 Hz. This level of dc performance along with low input currents make the AD645 an excellent choice for high impedance applications where stability is of prime concern.

OFFSET NULL –IN

2

+IN

4

8 1

7

+V

7 +VS – IN

2

6

OUTPUT

6 OUTPUT TOP VIEW

3

5 OFFSET NULL

+ IN

AD645

5

4

OFFSET NULL

–V

NC = NO CONNECT

NOTE: CASE IS CONNECTED TO PIN 8

The AD645 is available in six performance grades. The AD645J and AD645K are rated over the commercial temperature range of 0°C to +70°C. The AD645A, AD645B, and the ultraprecision AD645C are rated over the industrial temperature range of –40°C to +85°C. The AD645S is rated over the military temperature range of –55°C to +125°C and is available processed to MIL-STD-883B. The AD645 is available in an 8-pin plastic mini-DIP, 8-pin header, or in die form. PRODUCT HIGHLIGHTS

1. Guaranteed and tested low frequency noise of 2 µV p max and 20 nV/√Hz at 100 Hz makes the AD645C ideal for low noise applications where a FET input op amp is needed. 2. Low VOS drift of 1 µV/°C max makes the AD645C an excellent choice for applications requiring ultimate stability. 3. Low input bias current and current noise (11 fA p 0.1 Hz to 10 Hz) allow the AD645 to be used as a high precision preamp for current output sensors such as photodiodes, or as a buffer for high source impedance voltage output sensors. 30

1k

25

NUMBER OF UNITS

VOLTAGE NOISE SPECTRAL DENSITY nV/ Hz

AD645

3

–VS

OFFSET NULL

8 NC

1

100

10

20

15 10

5

0

1.0 1

10

100 FREQUENCY – Hz

1k

10k

Figure 1. AD645 Voltage Noise Spectral Density vs. Frequency

–2.5

–2.0

–1.5

–1.0

–0.5

0.0

0.5

1.0

1.5

2.0

2.5

INPUT OFFSET VOLTAGE DRIFT– µV/ °C

Figure 2. Typical Distribution of Average Input Offset Voltage Drift (196 Units)

REV. B Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 617/329-4700 Fax: 617/326-8703


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