Dual, Low Noise, Wideband
Variable Gain Amplifiers
AD600/AD602
FEATURES
2 channels with independent gain control
Linear in dB gain response
2 gain ranges
AD600: 0 dB to 40 dB
AD602: –10 dB to +30 dB
Accurate absolute gain: ±0.3 dB
Low input noise: 1.4 nV/√Hz
Low distortion: −60 dBc THD at ±1 V output
High bandwidth: dc to 35 MHz (−3 dB)
Stable group delay: ±2 ns
Low power: 125 mW (maximum) per amplifier
Signal gating function for each amplifier
Drives high speed ADCs
MIL-STD-883-compliant and DESC versions available
FUNCTIONAL BLOCK DIAGRAM
GAT1
SCALING
REFERENCE
C1HI
C1LO
GAIN CONTROL
INTERFACE
0dB
–12.04dB
–6.02dB
–18.06dB
–22.08dB
–36.12dB
–42.14dB
PRECISION PASSIVE
INPUT ATTENUATOR
GATING
INTERFACE
V
G
A1OP
A1CM
RF2
2.24kΩ (AD600)
694Ω (AD602)
RF1
20Ω
FIXED-GAIN
AMPLIFIER
41.07dB (AD600)
31.07dB (AD602)
–30.1dB
A1HI
A1LO
500Ω
R-2R LADDER NETWORK
62.5Ω
Figure 1.
APPLICATIONS
Ultrasound and sonar time-gain controls
High performance audio and RF AGC systems
Signal measurement
GENERAL DESCRIPTION
The AD600/AD602
dual channel, low noise, variable gain
amplifiers are optimized for use in ultrasound imaging systems
but are applicable to any application requiring precise gain, low
noise and distortion, and wide bandwidth. Each independent
channel provides a gain of 0 dB to +40 dB in the AD600 and
−10 dB to +30 dB in the AD602. The lower gain of the AD602
results in an improved signal-to-noise ratio (SNR) at the output.
However, both products have the same 1.4 nV/√Hz input noise
spectral density. The decibel gain is directly proportional to the
control voltage, accurately calibrated, and supply and
temperature stable.
To achieve the difficult performance objectives, a proprietary
circuit form, the X-AMP®, was developed. Each channel of the
X-AMP comprises a variable attenuator of 0 dB to −42.14 dB
followed by a high speed fixed gain amplifier. In this way, the
amplifier never has to cope with large inputs and can benefit
from the use of negative feedback to precisely define the gain
and dynamics. The attenuator is realized as a 7-stage R-2R
ladder network having an input resistance of 100 Ω, laser
trimmed to ±2%. The attenuation between tap points is 6.02 dB;
the gain-control circuit provides continuous interpolation between
these taps. The resulting control function is linear in dB.
Rev. E
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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
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The gain-control interfaces are fully differential, providing an
input resistance of ~15 MΩ and a scale factor of 32 dB/V (that
is, 31.25 mV/dB) defined by an internal voltage reference. The
response time of this interface is less than 1 μs. Each channel
also has an independent gating facility that optionally blocks
signal transmission and sets the dc output level to within a few
millivolts of the output ground. The gating control input is
TTL- and CMOS-compatible.
The maximum gain of the AD600 is 41.07 dB, and the
maximum gain of the AD602 is 31.07 dB; the −3 dB bandwidth
of both models is nominally 35 MHz, essentially independent of
the gain. The SNR for a 1 V rms output and a 1 MHz noise
bandwidth is typically 76 dB for the AD600 and 86 dB for the
AD602. The amplitude response is flat within ±0.5 dB from
100 kHz to 10 MHz; over this frequency range, the group delay
varies by less than ±2 ns at all gain settings.
Each amplifier channel can drive 100 Ω load impedances with
low distortion. For example, the peak specified output is ±2.5 V
minimum into a 500 Ω load or ±1 V into a 100 Ω load. For a
200 Ω load in shunt with 5 pF, the total harmonic distortion for
a ±1 V sinusoidal output at 10 MHz is typically −60 dBc.
The AD600J/AD602J are specified for operation from 0°C to 70°C
and are available in 16-lead PDIP (N) and 16-lead SOIC_W
packages. The AD600A/AD602A are specified for operation from
−40°C to +85°C and are available in 16-lead CERDIP (Q) and
16-lead SOIC_W packages. The AD600S/ AD602S are specified
for operation from −55°C to +125°C, are available in a 16-lead
CERDIP (Q) package, and are MIL-STD-883-compliant. The
AD600S/AD602S are also available under DESC SMD 5962-94572.
1
Patented.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.461.3113
©2006 Analog Devices, Inc. All rights reserved.
00538-001
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