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PDF AD797 Data sheet ( Hoja de datos )
| Número de pieza | AD797 | |
| Descripción | Ultralow Distortion/ Ultralow Noise Op Amp | |
| Fabricantes | Analog Devices | |
| Logotipo |  |
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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
1.0 μV/°C VOS 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
Table 1. Low Noise Op Amps
Voltage Noise
0.9 nV
Single
AD797
Dual
Quad
1.1 nV
AD8597
AD8599
1.8 nV
ADA4004-1
ADA4004-2
ADA4004-4
Ultralow Distortion,
Ultralow Noise Op Amp
AD797
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.
5
4
3
2
1
0
10 100 1k 10k 100k 1M 10M
FREQUENCY (Hz)
Figure 1. AD797 Voltage Noise Spectral Density
2.8 nV
AD8675/ADA4075-2
AD8676
3.2 nV
OP27
OP270
OP470
3.8 nV
AD8671
AD8672
AD8674
Rev. K
Document Feedback
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 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.
Trademarksandregisteredtrademarksarethepropertyoftheirrespectiveowners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700 ©1992–2015 Analog Devices, Inc. All rights reserved.
Technical Support
www.analog.com
1 page  
Data Sheet
ABSOLUTE MAXIMUM RATINGS
Table 3.
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)
Ratings
±18 V
±VS
±0.7 V
Indefinite within
maximum internal
power dissipation
−65°C to +125°C
−40°C to +85°C
300°C
1 The AD797 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.
Stresses at or above those listed under Absolute Maximum
Ratings may cause permanent damage to the product. This is a
stress rating only; functional operation of the product at these
or any other conditions above those indicated in the operational
section of this specification is not implied. Operation beyond
the maximum operating conditions for extended periods may
affect product reliability.
AD797
PIN CONFIGURATION
OFFSET NULL 1
–IN 2
+IN 3
AD797 8
7
6
DECOMPENSATION
AND DISTORTION
NEUTRALIZATION
+VS
OUTPUT
–VS 4 TOP VIEW 5 OFFSET NULL
Figure 2. 8-Lead Plastic Dual In-Line Package [PDIP] and
8-Lead Standard Small Outline Package [SOIC]
THERMAL RESISTANCE
θJA is specified for the device soldered on a 4-layer JEDEC
standard printed circuit board (PCB) with zero airflow for the
SOIC package, and a 2-layer JEDEC standard printed circuit
board (PCB) with zero airflow for the PDIP package.
Table 4. Thermal Resistance
Package Type
8-Lead SOIC (R-8)
8-Lead PDIP (N-8)
θJA θJC Unit
120 43 °C/W
103 50 °C/W
ESD CAUTION
Rev. K | Page 5 of 19
5 Page 
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 com-
pensation components. Slew rate and settling performance are
usually compromised, and dynamic performance is not adequate
beyond audio frequencies. As can be seen in Figure 31, the first
stage gain is rolled off at high frequencies by the compensation
network. Second stage noise and distortion then appears at the
input and degrade performance. The AD797, on the other hand,
uses a single ultrahigh gain stage to achieve dc as well as dynamic
precision. As shown in the simplified schematic (Figure 32),
Node A, Node B, and Node C track the input voltage, forcing
the operating points of all pairs of devices in the signal path to
match. By exploiting the inherent matching of devices fabricated on
the same IC chip, high open-loop gain, CMRR, PSRR, and low
VOS are guaranteed by pairwise device matching (that is, NPN
to NPN and PNP to PNP), not by an absolute parameter such as
beta and the early voltage.
gm
R1
BUFFER
C1
GAIN = gm × R1 × 5 × 106
a.
C2
VOUT
RL
gm
R1
A2
C1
A3
BUFFER
VOUT
RL
R2
GAIN = gm × R1 × A2 × A3
b.
Figure 31. Model of AD797 vs. That of a Typical Three-Stage Amplifier
VCC
R2 R3 CN
R1
Q4
Q3 Q7
I5
Q10
AB
+IN –IN
Q1 Q2
Q5
Q6 CC Q12 Q8
Q9
Q11
VOUT
I6
I1 C I7
I4
VSS
Figure 32. AD797 Simplified Schematic
This matching benefits not just dc precision, but, because it holds
up dynamically, both distortion and settling time are also reduced.
This single stage has a voltage gain of >5 × 106 and VOS < 80 μV,
while at the same time providing a THD + noise of less than
−120 dB and true 16-bit settling in less than 800 ns.
The elimination of second-stage noise effects has the additional
benefit of making the low noise of the AD797 (<0.9 nV/√Hz)
extend to beyond 1 MHz. This means new levels of perform-
ance for sampled data and imaging systems. All of this
performance as well as load drive in excess of 30 mA are made
possible by the Analog Devices, Inc., advanced complementary
bipolar (CB) process.
Another unique feature of this circuit is that the addition of a
single capacitor, CN (see Figure 32), enables cancellation of
distortion due to the output stage. This can best be explained by
referring to a simplified representation of the AD797 using
idealized blocks for the different circuit elements (Figure 33).
A single equation yields the open-loop transfer function of this
amplifier; solving it at Node B yields
VOUT
VIN
CN
A
gm
j CN
j CC
A
j
where:
gm is the transconductance of Q1 and Q2.
A is the gain of the output stage (~1).
VOUT is voltage at the output.
VIN is differential input voltage.
When CN is equal to CC, the ideal single-pole op amp response
is attained:
VOUT g m
VIN jC
In Figure 33, the terms of Node A, which include the properties of
the output stage, such as output impedance and distortion, cancel
by simple subtraction. Therefore, the distortion cancellation does
not affect the stability or frequency response of the amplifier. With
only 500 μA of output stage bias, the AD797 delivers a 1 kHz
sine wave into 60 Ω at 7 V rms with only 1 ppm of distortion.
I1 I2
CN
AB
+IN
Q1
–IN
Q2
CURRENT
MIRROR
I3 C I4
CC
1
A
Figure 33. AD797 Block Diagram
VOUT
Rev. K | Page 11 of 19
11 Page | ||
| Páginas | Total 19 Páginas | |
| PDF Descargar | [ Datasheet AD797.PDF ] | |
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