GENERAL DESCRIPTION

The AD8325 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 59.45 dB range resulting in gain changes of 0.7526 dB/LSB.

FEATURES

Supports DOCSIS Standard for Reverse Path Transmission

Gain Programmable in 0.75 dB Steps Over a 59.45 dB Range

Low Distortion at 61 dBmV Output

–57 dBc SFDR at 21 MHz

–55 dBc SFDR at 42 MHz

Output Noise Level

–48 dBmV in 160 kHz

Maintains 75 Ω Output Impedance Transmit Enable and Transmit Disable Modes

Upper Bandwidth: 100 MHz (Full Gain Range)

5 V Supply Operation

Supports SPI Interfaces

APPLICATIONS

Gain-Programmable Line Driver DOCSIS High-Speed Data Modems Interactive Cable Set-Top Boxes PC Plug-in Cable Modems

General-Purpose Digitally Controlled Variable Gain Block