REV. 0

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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. No license is granted by implication or otherwise

under any patent or patent rights of Analog Devices.

a

AD8367

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.

Tel: 781/329-4700

www.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

VPSO

VPSI

HPFL

ICOM

DECL

VOUT

ENBL

OCOM

DETO

GAIN

MODE

INPT

ICOM

ICOM

SQUARE

LAW

DETECTOR

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

200

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’

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

The analog gain-control interface is very simple to use. It is

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

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.