800 MHz, Linear-in-dB
VGA with AGC Detector
AD8368
FEATURES
FUNCTIONAL BLOCK DIAGRAM
VPSO
MODE VPSO VPSI VPSI VPSI VPSI VPSI
Analog variable gain range: −12 dB to +22 dB
Linear-in-dB scaling: 37.5 dB/V
3 dB bandwidth: 800 MHz @ VGAIN = 0.5 V
Integrated rms detector
10
21
9
11
12
22
23
13
16
6
ICOM
OCOM
GAIN
AD8368
1
GAIN INTERPOLATOR
FIXED-GAIN
AMPLIFIER
OUTPUT
BUFFER
24 ENBL
P1dB: 16 dBm @ 140 MHz
7
OCOM
Output IP3: 33 dBm @ 140 MHz
8
3
OUTP
HPFL
DECL
DECL
g
STAGES
m
Noise figure at maximum gain: 9.5 dB @ 140 MHz
Input and output impedances: 50 Ω
Single-supply voltage from 4.5 V to 5.5 V
RoHS-compliant, 24-lead LFCSP
0dB –2dB –4dB
–36dB
4
REF
19
17
18
20
INPT
ICOM
ICOM
ICOM
14
50Ω
DECL
–
+
15 DECL
2
X
ATTENUATOR LADDER
2
5
APPLICATIONS
DETO
DETI
Complete IF AGC amplifiers
Gain trimming and leveling
Cellular base stations
Figure 1.
Point-to-point radio links
RF instrumentation
GENERAL DESCRIPTION
The AD8368 is a variable gain amplifier (VGA) with analog
linear-in-dB gain control that can be used from low frequencies
to 800 MHz. Its excellent gain range, conformance, and flatness
are attributed to the Analog Devices, Inc. X-AMP® architecture,
an innovative technique for implementing high performance
variable gain control.
By connecting MODE to ground and using the on-board rms
detector, the AD8368 can be configured as a complete AGC
system with RSSI. The output power is accurately leveled to
the internal default setpoint of 63 mV rms (−11 dBm referenced
to 50 Ω), independent of the waveform crest factor. Because
the uncommitted detector input is available at DETI, the AGC
loop can level the signal at the AD8368 output or at any other
point in the signal chain over a maximum input power range
of 34 dB. Furthermore, the setpoint level can be raised by dividing
down the output signal before applying it to the detector.
The gain range of −12 dB to +22 dB is scaled accurately to
37.5 dB/V with excellent conformance error. The AD8368 has
a 3 dB bandwidth of 800 MHz that is nominally independent
of gain setting. At 140 MHz, the OIP3 is 33 dBm at maximum
gain. The output noise floor is −143 dBm/Hz, which corresponds
to a 9.5 dB noise figure at maximum gain. The single-ended
input and output impedances are nominally 50 Ω.
The AD8368 operates from a supply voltage of 4.5 V to 5.5 V
and consumes 60 mA of current. It can be fully powered down
to <3 mA by grounding the ENBL pin. The AD8368 is fabricated
using the Analog Devices proprietary SiGe SOI complementary
bipolar IC process. It is available in a 24-lead LFCSP and
operates over the industrial temperature range of −40°C to
+85°C. Application boards are available upon request.
The gain of the AD8368 can be configured to be an increasing
or decreasing function of the gain control voltage depending
on whether the MODE pin is pulled to the positive supply or
to ground, respectively. When MODE is pulled high, the
AD8368 operates as a typical VGA with increasing gain.
Rev. A
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.
Trademarks and registeredtrademarks arethe property of their respective owners.
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 ©2006-2007 Analog Devices, Inc. All rights reserved.
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