REV.0
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a
AD8367
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700www.analog.com
Fax: 781/326-8703 © Analog Devices, Inc., 2001
500 MHz, Linear-in-dB VGA
with AGC Detector
FUNCTIONAL BLOCK DIAGRAM
GAUSSIAN INTERPOLATOR
AD8367
VPSOVPSI
HPFL
ICOM
DECL
VOUT
ENBL
OCOM
DETOGAINMODE
INPT
ICOM
ICOM
SQUARE
LAW
DETECTOR
g
m
CELLS
9-STAGE ATTENUATOR BY 5dB BIAS
FEATURES
Broad Range Analog Variable Gain
–2.5 dB to +42.5 dB
3 dB Cutoff Frequency of 500 MHz
Gain Up and Gain Down Modes
Linear-in-dB, Scaled 20 mV/dB
Resistive Ground Referenced Input
Nominal Z
IN
H11549 200 H9024
On-Chip Square-Law Detector
Single-Supply Operation: 2.7 V to 5.5 V
APPLICATIONS
Cellular Base Station
Broadband Access
Power Amplifier Control Loops
Complete, Linear IF AGC Amplifiers
High-Speed Data I/O
GENERAL DESCRIPTION
The AD8367 is a high-performance 45 dB variable gain ampli-
fier with linear-in-dB gain control for use from low frequencies
up to several hundred megahertz. The range, flatness, and accu-
racy of the gain response are achieved using Analog Devices’
X-AMP
®
architecture, the most recent in a series of powerful
proprietary concepts for variable gain applications, which far
surpasses what can be achieved using competing techniques.
The input is applied to a 200 Ω resistive ladder network, having
nine sections each of 5 dB loss, for a total attenuation of 45 dB.
At maximum gain, the first tap is selected; at progressively lower
gains, the tap moves smoothly and continuously toward higher
attenuation values. The attenuator is followed by a 42.5 dB
fixed gain feedback amplifier—essentially an operational ampli-
fier with a gain bandwidth product of 100 GHz—and is very
linear, even at high frequencies. The output third order intercept is
+20 dBV at 100 MHz (+27 dBm re 200 Ω), measured at an
output level of 1 V p-p with V
S
= 5 V.
The analog gain-control interface is very simple to use. It is
scaled at 20 mV/dB, and the control voltage, V
GAIN
, runs from
50 mV at –2.5 dB to 950 mV at +42.5 dB. In the inverse-gain
mode of operation, selected by a simple pin-strap, the gain
decreases from +42.5 dB at V
GAIN
= 50 mV to –2.5 dB at
V
GAIN
= 950 mV. This inverse mode is needed in AGC applications,
which are supported by the integrated square-law detector,
whose set point is chosen to level the output to 354 mV rms,
regardless of the waveshape. A single external capacitor sets up
the loop averaging time.
The AD8367 may be powered on or off by a voltage applied to
the ENBL pin. When this voltage is at a logic LO, the total power
dissipation drops to the milliwatt range. For a logic HI, the chip
powers-up rapidly to its normal quiescent current of 26 mA at
25°C. The AD8367 is available in a 14-lead TSSOP package for
the industrial temperature range of –40°C to +85°C.
X-AMP is a registered trademark of Analog Devices, Inc.