800 MHz, Linear-in-dB
VGA with AGC Detector
AD8368
Rev. 0
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 registered trademarks are the 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 Analog Devices, Inc. All rights reserved.
FEATURES
Analog variable gain range: −12 db to +22 dB
Linear-in-dB scaling: 37.5 dB/V
3 dB bandwidth: 800 MHz @ V
GAIN
= 0.5 V
Integrated rms detector
P1 dB: 16 dBm @ 140 MHz
Output IP3: 33 dBm @ 140 MHz
Noise figure at maximum gain: 9.5 dB @ 140 MHz
Input and output impedances: 50 Ω
Single-supply voltages from 4.5 V to 5.5 V
RoHS-compliant, 24-lead LFCSP
APPLICATIONS
Complete IF AGC amplifiers
Gain trimming and leveling
Cellular base station
Point-to-point radio links
RF instrumentation
FUNCTIONAL BLOCK DIAGRAM
05907-001
9
V
PSO
11
V
PSI
12
V
PSI
22
V
PSI
23
V
PSI
13
V
PSI
24
ENBL
8
OUT
P
3
HPFL
4
DECL
14
DECL
15
DECL
20
ICOM
18
ICOM
17
ICOM
19
INPT
7
OCOM
1
GAIN
6
OCOM
16
ICOM
10
V
PSO
21
MODE
2
DETO
5
DETI
REF
X
2
–
+
AD8368
ATTENUATOR LADDER
DECL
50Ω
0dB –2dB –4dB –36dB
GAIN INTERPOLATOR
g
m
STAGES
FIXED-GAIN
AMPLIFIER
OUTPUT
BUFFER
Figure 1.
GENERAL DESCRIPTION
The AD8368 is a variable gain amplifier 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 Analog Devices’ X-AMP® architecture, an
innovative technique for implementing high performance
variable gain control.
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 maxi-
mum 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 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. 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 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 Analog Devices’ proprietary SiGe SOI
complementary bipolar IC process. It is available in a 24-lead
CSP and operates over the industrial temperature range of
−40°C to +85°C. Application boards are available upon request.
剩余19页未读，继续阅读
资源评论
