Datasheet

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Ultralow Distortion,

Ultralow Noise Op Amp

Data Sheet

AD797

Rev. I Document Feedback

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FEATURES

Low noise

0.9 nV/√Hz typical (1.2 nV/√Hz maximum) 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 maximum input offset voltage

1.0 μV/°C V

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

Σ-Δ ADC/DAC buffers

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 in audio bandwidths

give the AD797 the wide dynamic range necessary for preamps

in microphones and mixing consoles.

Furthermore, the AD797 has an excellent slew rate of 20 V/μs

and a 110 MHz gain bandwidth, which makes it highly suitable

for low frequency ultrasound applications.

The AD797 is also useful in infrared (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 Σ-Δ ADCs or the outputs of

high resolution DACs, especially when the device is used in

critical applications such as seismic detection or in 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.

00846-002

10M

100

1M100k10k1k

FREQUENCY (Hz)

INPUT VOLTAGE NOISE (nV/√Hz)

Figure 1. AD797 Voltage Noise Spectral Density

Table 1. Low Noise Op Amps

Voltage Noise 0.9 nV 1.1 nV 1.8 nV 2.8 nV 3.2 nV 3.8 nV

Single AD797 AD8597 ADA4004-1 AD8675/ADA4075-2 OP27 AD8671

Dual AD8599 ADA4004-2 AD8676 OP270 AD8672

Quad ADA4004-4 OP470 AD8674

Summary of content (20 pages)

PAGE 1
Ultralow Distortion, Ultralow Noise Op Amp AD797 Data Sheet FEATURES Low noise 0.9 nV/√Hz typical (1.2 nV/√Hz maximum) 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 maximum input offset voltage 1.
PAGE 2
AD797 Data Sheet TABLE OF CONTENTS Features .............................................................................................. 1 Noise and Source Impedance Considerations ........................... 12 Applications ....................................................................................... 1 Low Frequency Noise ................................................................ 12 General Description .........................................................................
PAGE 3
Data Sheet AD797 SPECIFICATIONS TA = 25°C and VS = ±15 V dc, unless otherwise noted. Table 2. AD797A Parameter INPUT OFFSET VOLTAGE Conditions Supply Voltage (V) ±5 V, ±15 V Min TMIN to TMAX Offset Voltage Drift INPUT BIAS CURRENT ±5 V, ±15 V ±5 V, ±15 V TMIN to TMAX INPUT OFFSET CURRENT OPEN-LOOP GAIN DYNAMIC PERFORMANCE Gain Bandwidth Product –3 dB Bandwidth Full Power Bandwidth1 Slew Rate Settling Time to 0.
PAGE 4
AD797 Data Sheet AD797A Parameter INPUT CHARACTERISTICS Input Resistance Differential Common Mode Input Capacitance Differential 4 Common Mode OUTPUT RESISTANCE POWER SUPPLY Operating Range Quiescent Current Conditions Supply Voltage (V) Min AV = 1, f = 1 kHz Typ Max 2 3 Rev. I | Page 4 of 20 Typ Max Unit 7.5 100 kΩ MΩ 20 5 3 20 5 3 pF pF mΩ ±18 10.5 V mA 8.2 ±18 10.5 Full power bandwidth = slew rate/2π VPEAK. Specified using external decompensation capacitor.
PAGE 5
Data Sheet AD797 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION Parameter Supply Voltage Input Voltage Differential Input Voltage1 Output Short-Circuit Duration Storage Temperature Range (N, R Suffix) Operating Temperature Range Lead Temperature (Soldering 60 sec) 1 Ratings ±18 V ±VS ±0.
PAGE 6
AD797 Data Sheet TYPICAL PERFORMANCE CHARACTERISTICS 10 5 0 0 5 10 15 20 SUPPLY VOLTAGE (±V) HORIZONTAL SCALE (5sec/DIV) Figure 3. Input Common-Mode Voltage Range vs. Supply Voltage Figure 6. 0.1 Hz to 10 Hz Noise 0 10 +VOUT –VOUT 5 0 0 5 10 15 20 SUPPLY VOLTAGE (±V) –0.5 –1.0 –1.5 –2.0 –60 –40 –20 0 20 40 60 80 100 120 140 TEMPERATURE (°C) Figure 4. Output Voltage Swing vs. Supply Voltage 00846-008 INPUT BIAS CURRENT (µA) 15 00846-005 Figure 7.
PAGE 7
Data Sheet AD797 +125°C 9 +25°C 8 7 –55°C 0 5 15 10 20 SUPPLY VOLTAGE (±V) PSR –SUPPLY 100 150 125 80 CMR 60 100 40 75 1 10 100 1k 10k 100k 50 1M FREQUENCY (Hz) Figure 9. Quiescent Supply Current vs. Supply Voltage Figure 12. Power Supply and Common-Mode Rejection vs. Frequency –60 12 f = 1kHz RL = 600Ω G = +10 RL = 600Ω G = +10 f = 10kHz NOISE BW = 100kHz THD + NOISE (dB) 9 6 –80 VS = ±5V –100 3 0 0 ±5 ±15 ±10 ±20 SUPPLY VOLTAGE (±V) –120 0.01 0.
PAGE 8
AD797 Data Sheet 100 3 2 1 0 1k 10k 10M 1M 100k FREQUENCY (Hz) 1 1 10 100 1k 10k FREQUENCY (Hz) Figure 18. Current Noise Density VS = ±15 V Figure 15. Input Voltage Noise Spectral Density 120 120 35 100 PHASE MARGIN 80 60 40 GAIN 20 40 *RS = 100 WITHOUT RS* 20 *SEE FIGURE 26.
PAGE 9
Data Sheet AD797 50mV 100ns 100 90 10 1 WITHOUT CN* 0.1 10 WITH CN* 0% 00846-024 *SEE FIGURE 33. 100 1k 10k 100k 1M FREQUENCY (Hz) Figure 24. Inverter Small-Signal Pulse Response Figure 21. Magnitude of Output Impedance vs. Frequency 20pF 100Ω 1kΩ +VS ** +VS 2 * 1kΩ 2 AD797 7 AD797 3 VIN VOUT 6 VOUT 6 RS* 3 600Ω 4 ** 4 –VS * *VALUE OF SOURCE RESISTANCE (SEE THE NOISE AND SOURCE IMPEDANCE CONSIDERATIONS SECTION). **SEE FIGURE 36. –VS *SEE FIGURE 36. Figure 22.
PAGE 10
AD797 Data Sheet 50mV 100ns 100 100 90 90 10 0% 00846-027 10 0% 500ns 00846-029 50mV Figure 29. 16-Bit Settling Time Negative Input Pulse Figure 27. Follower Small-Signal Pulse Response –90 50mV 500ns THD (dB) 90 –100 0.001 –110 0.0003 –120 0.0001 THD (%) 100 00846-028 –130 100 300 1k 3k 10k 30k FREQUENCY (Hz) Figure 28. 16-Bit Settling Time Positive Input Pulse Figure 30. THD vs. Frequency Rev.
PAGE 11
Data Sheet AD797 THEORY OF OPERATION The architecture of the AD797 was developed to overcome inherent limitations in previous amplifier designs. Previous precision amplifiers used three stages to ensure high open-loop gain (see Figure 31) at the expense of additional frequency compensation components. Slew rate and settling performance are usually compromised, and dynamic performance is not adequate beyond audio frequencies.
PAGE 12
AD797 Data Sheet NOISE AND SOURCE IMPEDANCE CONSIDERATIONS LOW FREQUENCY NOISE The AD797 ultralow voltage noise of 0.9 nV/√Hz is achieved with special input transistors running at nearly 1 mA of collector current. Therefore, it is important to consider the total inputreferred noise (eNtotal), which includes contributions from voltage noise (eN), current noise (iN), and resistor noise (√4 kTRS). Analog Devices specifies low frequency noise as a peak-to-peak quantity in a 0.1 Hz to 10 Hz bandwidth.
PAGE 13
Data Sheet AD797 CL BYPASSING CONSIDERATIONS Taking full advantage of the very wide bandwidth and dynamic range capabilities of the AD797 requires some precautions. First, multiple bypassing is recommended in any precision application. A 1.0 μF to 4.7 μF tantalum in parallel with 0.1 μF ceramic bypass capacitors are sufficient in most applications. When driving heavy loads, a larger demand is placed on the supply bypassing.
PAGE 14
AD797 Data Sheet The I-to-V converter is a special case of the follower configuration. When the AD797 is used in an I-to-V converter, for example as a DAC buffer, the circuit shown in Figure 40 should be used. The value of CL depends on the DAC, and if CL is greater than 33 pF, a 100 Ω series resistor is required. A bypassed balancing resistor (RS and CS) can be included to minimize dc errors.
PAGE 15
Data Sheet AD797 TO TEKTRONIX 7A26 OSCILLOSCOPE 1MΩ PREAMP INPUT SECTION The benefits of adding C1 are evident for closed-loop gains of ≥100. A maximum value of ≈33 pF at gains of ≥1000 is recommended. At a gain of 1000, the bandwidth is 450 kHz. 20pF Table 8 and Figure 46 summarize the performance of the AD797 with distortion cancellation and decompensation. 4.26kΩ 226Ω (VIA LESS THAN 1FT 50Ω COAXIAL CABLE) 2 – A2 AD829 3 250Ω 6 7 + 50pF 2× HP2835 4 2× HP2835 R1 VERROR × 5 R2 0.
PAGE 16
AD797 Data Sheet –90 1k 3k 10k 30k 100k 00846-048 300 7 300k FREQUENCY (Hz) 2 Figure 49. Total Harmonic Distortion (THD) vs. Frequency for Differential Line Receiver 8 VOUT 6 A General-Purpose ATE/Instrumentation I/O Driver 4 3 ** The ultralow noise and distortion of the AD797 can be combined with the wide bandwidth, slew rate, and load drive of a current feedback amplifier to yield a very wide dynamic range general-purpose driver.
PAGE 17
Ultrasound/Sonar Imaging Preamp –30 –40 VOUT (dB Re 1V/µA) The AD600 variable gain amplifier provides the time-controlled gain (TCG) function necessary for very wide dynamic range sonar and low frequency ultrasound applications. Under some circumstances, it is necessary to buffer the input of the AD600 to preserve its low noise performance. To optimize dynamic range, this buffer should have a maximum of 6 dB of gain. The combination of low noise and low gain is difficult to achieve.
PAGE 18
AD797 Data Sheet OUTLINE DIMENSIONS 0.400 (10.16) 0.365 (9.27) 0.355 (9.02) 8 5 1 4 0.280 (7.11) 0.250 (6.35) 0.240 (6.10) 0.100 (2.54) BSC 0.325 (8.26) 0.310 (7.87) 0.300 (7.62) 0.060 (1.52) MAX 0.210 (5.33) MAX 0.015 (0.38) MIN 0.150 (3.81) 0.130 (3.30) 0.115 (2.92) SEATING PLANE 0.022 (0.56) 0.018 (0.46) 0.014 (0.36) 0.195 (4.95) 0.130 (3.30) 0.115 (2.92) 0.015 (0.38) GAUGE PLANE 0.014 (0.36) 0.010 (0.25) 0.008 (0.20) 0.430 (10.92) MAX 0.005 (0.13) MIN 0.070 (1.78) 0.060 (1.52) 0.045 (1.
PAGE 19
Data Sheet AD797 ORDERING GUIDE Model 1 AD797ANZ AD797AR AD797AR-REEL AD797AR-REEL7 AD797ARZ AD797ARZ-REEL AD797ARZ-REEL7 AD797BR AD797BR-REEL AD797BR-REEL7 AD797BRZ AD797BRZ-REEL AD797BRZ-REEL7 1 Temperature Range −40°C to +85°C −40°C to +85°C −40°C to +85°C −40°C to +85°C −40°C to +85°C −40°C to +85°C −40°C to +85°C −40°C to +85°C −40°C to +85°C −40°C to +85°C −40°C to +85°C −40°C to +85°C −40°C to +85°C Package Description 8-Lead Plastic Dual In-Line Package [PDIP] 8-Lead Standard Small Outline Packa