REV. 0

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a

AD8323

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., 2000

5 V CATV Line Driver Fine Step

Output Power Control

FUNCTIONAL BLOCK DIAGRAM

DIFF OR

SINGLE

INPUT

AMP

ATTENUATION

CORE

75

8

8

8

R1

R2

AD8323

DATEN

DATA

CLK

GND (11 PINS)

PD

SLEEP

BUFFER

DECODE

DATA LATCH

SHIFT

REGISTER

POWER-DOWN

LOGIC

POWER

AMP

BYP

FEATURES

Supports DOCSIS Standard for Reverse Path

Transmission

Gain Programmable in 0.75 dB Steps Over a 53.5 dB

Range

Low Distortion at 60 dBmV Output

–56 dBc SFDR at 21 MHz

–55 dBc SFDR at 42 MHz

Output Noise Level

–48 dBmV in 160 kHz

Maintains 75

Output Impedance

Power-Up and Power-Down Condition

Upper Bandwidth: 100 MHz (Full Gain Range)

5 V Supply Operation

Supports SPI Interfaces

APPLICATIONS

Gain-Programmable Line Driver

HFC High-Speed Data Modems

Interactive Set-Top Boxes

PC Plug-in Modems

General-Purpose Digitally Controlled Variable Gain Block

GENERAL DESCRIPTION

The AD8323 is a low-cost, digitally controlled, variable gain ampli-

fier optimized for coaxial line driving applications such as cable

modems that are designed to the MCNS-DOCSIS upstream

standard. An 8-bit serial word determines the desired output gain

over a 53.5 dB range resulting in gain changes of 0.7526 dB/LSB.

The AD8323 comprises a digitally controlled variable attenuator

of 0 dB to –53.5 dB, which is preceded by a low noise, fixed

gain buffer and is followed by a low distortion high power am-

plifier. The AD8323 accepts a differential or single-ended input

signal. The output is specified for driving a 75

Ω load, such as

coaxial cable.

Distortion performance of –56 dBc is achieved with an output

level up to 60 dBmV at 21 MHz bandwidth. A key performance

and cost advantage of the AD8323 results from the ability to main-

tain a constant 75

Ω output impedance during power-up and

power-down conditions. This eliminates the need for external 75

Ω

termination, resulting in twice the effective output voltage when

compared to a standard operational amplifier. In addition, this

device has a sleep mode function that reduces the quiescent

current to 4 mA.

The AD8323 is packaged in a low-cost 28-lead TSSOP, operates

from a single 5 V supply, and has an operational temperature

range of –40

°C to +85°C.

GAIN CONTROL – DEC Code

–50

0

–55

–60

–65

–70

–75

8

1624

32

4048

56

HD3

HD2

64

72

Figure 1. Harmonic Distortion vs. Gain Control