ANALOG DEVICES AD797 Service Manual

Ultralow Distortion,

Ultralow Noise Op Amp

FEATURES CONNECTION DIAGRAM

Low noise

0.9 nV/√Hz typ (1.2 nV/√Hz max) input voltage noise at 1 kHz

50 nV p-p input voltage noise, 0.1 Hz to 10 Hz Low distortion

−120 dB total harmonic distortion at 20 kHz

Excellent AC characteristics

800 ns settling time to 16 bits (10 V step) 110 MHz gain bandwidth (G = 1000) 8 MHz bandwidth (G = 10) 280 kHz full power bandwidth at 20 V p-p 20 V/μs slew rate

Excellent DC precision

80 μV max input offset voltage

1.0 μV/°C V

OS

drift Specified for ±5 V and ±15 V power supplies High output drive current of 50 mA

APPLICATIONS

Professional audio preamplifiers IR, CCD, and sonar imaging systems Spectrum analyzers Ultrasound preamplifiers Seismic detectors ΣΔ ADC/DAC buffers

–IN +IN 3

–V

S

1 2

4

AD797

TOP VIEW

OFFSET NULL

Figure 1. 8-Lead Plastic Dual In-Line Package [PDIP] and

8-Lead Standard Small Outline Package [SOIC_N]

GENERAL DESCRIPTION

The AD797 is a very low noise, low distortion operational amplifier ideal for use as a preamplifier. The low noise of

0.9 nV/√Hz and low total harmonic distortion of −120 dB at audio bandwidths give the AD797 the wide dynamic range necessary for preamps in microphones and mixing consoles.

Furthermore, the AD797’s excellent slew rate of 20 V/μs and 110 MHz gain bandwidth make it highly suitable for low frequency ultrasound applications.

The AD797 is also useful in IR and sonar imaging applications where the widest dynamic range is necessary. The low distortion and 16-bit settling time of the AD797 make it ideal for buffering the inputs to ΣΔ ADCs or the outputs of high resolution DACs especially when used in critical applications such as seismic detection and spectrum analyzers. Key features such as a 50 mA output current drive and the specified power supply voltage range of ±5 V to ±15 V make the AD797 an excellent general-purpose amplifier.

8 7 6 5

DECOMPENSATION AND DISTORTION NEUTRALIZATION

+V

S

OUTPUT OFFSET NULL

AD797

00846-001

5

4

Hz)

3

2

1

INPUT VOLTAGE NOISE (nV/

0

100

10

FREQUENCY (Hz)

10M

1M100k10k1k

00846-002

Figure 2. AD797 Voltage Noise Spectral Density

Rev. E

Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devi ces for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners.

–90

–100

–110

THD (dB)

–120

MEASUREMENT LIMIT

–130

300100

FREQUENCY (Hz)

Figure 3. THD vs. Frequency

100k30k10k3k1k

300k

0.001

0.0003

THD (%)

0.0001

00846-003

AD797

SPECIFICATIONS

@ TA = +25°C and VS = ±15 V dc, unless otherwise noted.

Table 1.

AD797A AD797B Parameter Conditions V Min Typ Max Min Typ Max Unit

INPUT OFFSET VOLTAGE ±5 V, ±15 V 25 80 10 40 μV T

Offset Voltage Drift ±5 V, ±15 V 0.2 1.0 0.2 0.6 μV/°C INPUT BIAS CURRENT ±5 V, ±15 V 0.25 1.5 0.25 0.9 μA T INPUT OFFSET CURRENT ±5 V, ±15 V 100 400 80 200 nA T OPEN-LOOP GAIN V R T R T @ 20 kHz1 DYNAMIC PERFORMANCE

Gain Bandwidth Product G = 1000 ±15 V 110 110 MHz

G = 1000

–3 dB Bandwidth G = 10 ±15 V 8 8 MHz

Full Power Bandwidth

1

R

Slew Rate R

Settling Time to 0.0015% 10 V step ±15 V 800 1200 800 1200 ns COMMON-MODE REJECTION VCM = CMVR ±5 V, ±15 V 114 130 120 130 dB T POWER SUPPLY REJECTION VS = ±5 V to ±18 V 114 130 120 114 dB T INPUT VOLTAGE NOISE f = 0.1 Hz to 10 Hz ±15 V 50 50 nV p-p f = 10 Hz ±15 V 1.7 1.7 2.5 nV/√Hz f = 1 kHz ±15 V 0.9 1.2 0.9 1.2 nV/√Hz f = 10 Hz to 1 MHz ±15 V 1.0 1.3 1.0 1.2 μV rms INPUT CURRENT NOISE f = 1 kHz ±15 V 2.0 2.0 pA/√Hz INPUT COMMON-MODE VOLTAGE RANGE ±15 V ±11 ±12 ±11 ±12 V ±5 V ±2.5 ±3 ±2.5 ±3 V OUTPUT VOLTAGE SWING R R R

Short-Circuit Current ±5 V, ±15 V 80 80 mA

Output Current3 ±5 V, ±15 V 30 50 30 50 mA TOTAL HARMONIC DISTORTION R f = 250 kHz, 3 V rms R f = 20 kHz, 3 V rms INPUT CHARACTERISTICS

Input Resistance (Differential) 7.5 7.5 kΩ

Input Resistance (Common Mode) 100 100 MΩ

Input Capacitance (Differential)4 20 20 pF

Input Capacitance (Common Mode) 5 5 pF

to T

MIN

MAX

to T

MIN

MAX

to T

MIN

MAX

= ±10 V ±15 V 1 20 2 20 V/μV

OUT

= 2 kΩ 1 6 2 10 V/μV

LOAD

to T

MIN

MAX

= 600 Ω 1 5 2 7 V/μV

LOAD

to T

MIN

MAX

2

50 125/180 30 60 μV

0.5 3.0 0.25 2.0 μA

120 600/700 120 300 nA

1 15 2 15 V/μV

14000 20000 14000 20000 V/V

15 V 450 450 MHz

VO = 20 V p-p,

= 1 kΩ ±15 V 280 280 kHz

LOAD

= 1 kΩ ±15 V 12.5 20 12.5 20 V/μs

LOAD

to T

MIN

MAX

to T

MIN

MAX

= 2 kΩ ±15 V ±12 ±13 ±12 ±13 V

LOAD

= 600 Ω ±15 V ±11 ±13 ±11 ±13 V

LOAD

= 600 Ω ±5 V ±2.5 ±3 ±2.5 ±3 V

LOAD

= 1 kΩ, CN = 50 pF ±15 V −98 –90 –98 –90 dB

LOAD

= 1 kΩ ±15 V –120 –110 –120 –110 dB

LOAD

110 120 114 120 dB

110 120 130 120 dB

Rev. E | Page 3 of 20

AD797

AD797A AD797B Parameter Conditions V Min Typ Max Min Typ Max Unit

OUTPUT RESISTANCE AV = +1, f = 1 kHz 3 3 mΩ POWER SUPPLY

Operating Range ±5 ±18 ±5 ±18 V Quiescent Current ±5 V, ±15 V 8.2 10.5 8.2 10.5 mA

1

Full Power Bandwidth = Slew Rate/2 π V

2

Specified using external decompensation capacitor; see Applications section.

3

Output current for |V – V | > 4 V, A > 200 kΩ.

4

Differential input capacitance consists of 1.5 pF package capacitance and 18.5 pF from the input differential pair.

S OUT OL

PEAK

.

Rev. E | Page 4 of 20

AD797

ABSOLUTE MAXIMUM RATINGS

Table 2.

Parameter Ratings

Supply Voltage ±18 V Internal Power Dissipation @ 25°C

1

Input Voltage ±V Differential Input Voltage

2

Output Short-Circuit Duration

S

±0.7 V Indefinite Within

Max Internal

Power Dissipation Storage Temperature Range (Cerdip) −65°C to +150°C Storage Temperature Range (N, R Suffix) −65°C to +125°C Operating Temperature Range

AD797A/B −40°C to +85°C Lead Temperature Range (Soldering 60 sec) 300°C

1

Internal Power Dissipation:

8-Lead SOIC = 0.9 W (T –25°C)/θ

8-Lead Plastic DIP and Cerdip = 1.3 W − (T –25°C)/θ

Thermal Characteristics

8-Lead Plastic DIP Package: θJA = 95°C/W

8-Lead Small Outline Package: θJA = 155°C/W

2

The AD797’s inputs are protected by back-to-back diodes. To achieve low noise, internal current limiting resistors are not incorporated into the design of this amplifier. If the differential input voltage exceeds ±0.7 V, the input current should be limited to less than 25 mA by series protection resistors. Note, however, that this degrades the low noise performance of the device.

A JA

Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.

ESD CAUTION

ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although these products feature proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality.

Rev. E | Page 5 of 20

AD797

TYPICAL PERFORMANCE CHARACTERISTICS

20

15

10

5

INPUT COMMON-MODE RANGE (±V)

VERTICAL SCALE (0.01μV/DIV)

0

5

10 15

SUPPLY VOLTAGE (±V)

Figure 4. Common-Mode Voltage Range vs. Supply

20

15

OUTPUT VOLTAGE SWING (±V)

10

–V

OUT

5

0

5

SUPPLY VOLTAGE (±V)

+V

OUT

10

Figure 5. Output Voltage Swing vs. Supply

30

VS= ±15V

20

00846-004

HORIZONTAL SCALE (5sec/DIV)

00846-007

Figure 7. 0.1 Hz to 10 Hz Noise

0

–0.5

–1.0

INPUT AS CURRENT (μA)

–1.5

00846-005

15

20

–2.0

–60 140–40 100 120806040200–20

TEMPERATURE (°C)

00846-008

Figure 8. Input Bias Current vs. Temperature

140

120

20

10

OUTPUT VOLTAGE SWING (V p-p)

0

10 100 10k1k

VS =±5

LOAD RESISTANCE (Ω)

Figure 6. Output Voltage Swing vs. Load Resistance

00846-006

Rev. E | Page 6 of 20

100

80

SHORT-CIRCUIT CURRENT (mA)

60

40

–60

SINK CURRENT

–40

TEMPERATURE (°C)

SOURCE CURRENT

Figure 9. Short-Circuit Current vs. Temperature

00846-009

140

6040200–20

80

120100

ANALOG DEVICES AD797 Service Manual

FEATURES CONNECTION DIAGRAM

APPLICATIONS

GENERAL DESCRIPTION

TABLE OF CONTENTS

SPECIFICATIONS

ABSOLUTE MAXIMUM RATINGS

ESD CAUTION

TYPICAL PERFORMANCE CHARACTERISTICS