Gain Programmable

a

CATV Line Driver

AD8321

FEATURES

FUNCTIONAL BLOCK DIAGRAM

Linear in dB Gain Response Over >53 dB Range

Drives Low Distortion >11 dBm Signal into 75

� Load:

VCC

GND

–53 dBc SFDR at 42 MHz

APPLICATIONS

Gain Programmable Line Driver

HFC High Speed Data Modems

Interactive CATV Set-Top Boxes

CATV Plant Test Equipment

AD8321

POWER-

DOWN/

SWITCH

INTER

ATTENUATOR CORE

INV

DATA SHIFT REGISTER

DATA LATCH

PWR

AMP

DATEN CLK

REVERSE

AMP

SDATA

General Purpose IF Variable Gain Block

DESCRIPTION

The AD8321 is packaged in a low cost 20-lead SOIC, operates

The AD8321 is a low cost digitally controlled variable gain

from a single +9 V supply, and has an operational temperature

amplifier optimized for coaxial line driving applications such as

range of –40

∞C to +85∞C.

cable modems that are designed to the DOCSIS

* (upstream)

Very Low Output Noise Level

Maintains Constant 75

� Output Impedance

Power-Up and Power-Down Condition

No Line Transformer Required

VIN+

Upper Bandwidth: 235 MHz (Min Gain)

VIN–

9V Single Supply Operation

Power-Down Functionality

Supports SPI Interface

Low Cost

VOUT

PD

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

over a 53.4 dB range, resulting in gain changes of 0.75 dB/LSB.

–40

The AD8321 comprises a digitally controlled variable attenuator

of 0 dB to –53.4 dB, which is preceded by a low noise, fixed

–50

4

137mV

–15dB

2MHz

p-p

m)

MAX

= 11d

GAIN)

Bm @

HD3

HD2

gain buffer and followed by a low distortion high power ampli­

fier. The AD8321 accepts a differential or single-ended input

signal. The output is specified for driving a 75

W load, such as

coaxial cable, although the AD8321 is capable of driving other

loads. Performance of –53 dBc is achieved with an output level

up to 11 dBm at 42 MHz bandwidth using a 9 V supply.

–60

–70

A key performance and cost advantage of the AD8321 results

from the ability to maintain a constant 75

W output impedance

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

the need for external 75

W termination, resulting in twice the

effective output voltage when compared to a standard opera­

tional amplifier, thus eliminating the need for a transformer.

*Data-Over-Cable Service Interface Specifications

REV. A

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. 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.

–80

–90

0

8

16

24

32

40

48

56

64

72

GAIN CONTROL – Decimal

Figure 1. Harmonic Distortion vs. Gain Control

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

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