REV. 0

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a

AD8320

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

Tel: 781/329-4700

World Wide Web Site: http://www.analog.com

Fax: 781/326-8703

© Analog Devices, Inc., 1998

Serial Digital Controlled

Variable Gain Line Driver

FEATURES

8-Bit Serial Gain Control

V/V/LSB Linear Gain Response

36 dB Gain Range

0.20 dB Gain Accuracy

Upper Bandwidth: 150 MHz

22 dBm 1 dB Compression Point (75

)

Drives Low Distortion Signals into 75

Load:

–57 dBc SFDR at 42 MHz and 12 dBm Out

–46 dBc SFDR at 42 MHz and 18 dBm Out

Single Supply Operation from 5 V to 12 V

Maintains 75

Output Impedance

Power-Up and Power-Down Condition

Supports SPI Input Control Standard

APPLICATIONS

Coaxial Cable Driver

HFC Cable Telephony Systems

HFC High Speed Data Modems

Interactive Set-Top Boxes

PC Plug-In Modems

High Performance Digitally Controlled Variable Gain

Block

DESCRIPTION

The AD8320 is a digitally controlled variable gain amplifier

optimized for coaxial line driving applications. An 8-bit serial

word determines the desired output gain over a 36 dB range

(256 gain levels). The AD8320 provides linear gain response.

The AD8320 is made up of a digitally controlled variable at-

tenuator of 0 dB to –36 dB, which is preceded by a low noise,

fixed gain buffer and followed by a low distortion high power

amplifier. The AD8320 has a 220

Ω input impedance and ac-

cepts a single-ended input signal with a specified analog input

level of up to 0.310 V p-p. The output is specified for driving a

75

Ω load, such as coaxial cable, although the AD8320 is ca-

pable of driving other loads. Distortion performance of –57 dBc

is achieved with an output level up to 12 dBm (3.1 V p-p) at

42 MHz, while –46 dBc distortion is achieved with an output

level up to 18 dBm (6.2 V p-p).

A key performance and cost advantage of the AD8320 results

from the ability to maintain a constant 75

Ω output impedance

during power-up and power-down conditions. This eliminates

the need for external 75

Ω back-termination, resulting in twice

the effective output voltage when compared to a standard opera-

tional amplifier. Additionally, the on-chip 75

Ω termination

results in low glitch output during power-down and power-up

transitions, eliminating the need for an external switch.

The AD8320 is packaged in a 20-lead SOIC and operates from

a single +5 V through +12 V supply and has an operational

temperature range of –40

°C to +85°C.

FREQUENCY – MHz

1

10

100

20

30

40

50

60

70

80

Figure 1. Worst Harmonic Distortion vs. Frequency for

FUNCTIONAL BLOCK DIAGRAM

POWER-

DOWN/

SWITCH

INTER.

PWR AMP

DATA SHIFT REGISTER

DATA LATCH

REVERSE

AMP

ATTENUATOR CORE

GND

VCC

VREF

VIN

REFERENCE

INV.

BUF.

DATEN CLK

SDATA

PD

VOUT

AD8320