GENERAL DESCRIPTION

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

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

ABSOLUTE MAXIMUM RATINGS*

Supply Voltage +VS

Pins 5, 9, 10, 19, 20, 23, 27 . . . . . . . . . . . . . . . . . . . . . . 6 V

Input Voltages

Pins 25, 26 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ±0.5 V

Pins 1, 2, 3, 6, 7 . . . . . . . . . . . . . . . . . . . . . –0.8 V to +5.5 V

Internal Power Dissipation

TSSOP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.9 W

Operating Temperature Range . . . . . . . . . . . –40°C to +85°C

Storage Temperature Range . . . . . . . . . . . . –65°C to +150°C

Lead Temperature, Soldering 60 seconds . . . . . . . . . . . 300°C