5 V CATV Line Driver Coarse Step
Output Power Control
Supports DOCSIS Standard for Reverse Path
Gain Programmable in 6.02 dB Steps over a 48.16 dB
Low Distortion at 60 dBmV Output
–63 dBc SFDR at 21 MHz
–57 dBc SFDR at 42 MHz
Output Noise Level
–47 dBmV in 160 kHz
Maintains 75 ⍀ Output Impedance
Transmit Enable and Transmit Disable Modes
Upper Bandwidth: 160 MHz (Full Gain Range)
5 V Supply Operation
Supports SPI Interfaces
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
FUNCTIONAL BLOCK DIAGRAM
VCC (5 PINS)
ZIN (SINGLE) = 800⍀
ZIN (DIFF) = 1.6k⍀
ZOUT = 75⍀
DATEN DATA CLK GND (5 PINS) TXEN SLEEP
The AD8327 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 48.16 dB range resulting in gain changes of
6.02 dB/major carry.
The AD8327 comprises a digitally controlled variable attenuator
of 0 dB to –48.16 dB, which is preceded by a low noise, fixed
gain buffer and followed by a low distortion, high power amplifier.
The AD8327 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 –63 dBc is achieved with an output
level up to 60 dBmV at 21 MHz bandwidth. A key performance
and cost advantage of the AD8327 results from the ability to
maintain a constant 75 Ω output impedance during Transmit
Enable and Transmit Disable conditions. In addition, this
device has a sleep mode function that reduces the quiescent
current to 5 mA.
The AD8327 is packaged in a low-cost 20-lead TSSOP, operates
from a single 5 V supply, and has an operational temperature
range of –40°C to +85°C.
VOUT = 60dBmV @ MAX GAIN
15 25 35 45 55
FUNDAMENTAL FREQUENCY – MHz
Figure 1. Harmonic Distortion vs. Frequency
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© Analog Devices, Inc., 2001