
REV. 0
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a
AD8327
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
Fax: 781/326-8703
Analog Devices, Inc., 2001
5 V CATV Line Driver Coarse Step
Output Power Control
FUNCTIONAL BLOCK DIAGRAM
DIFF OR
SINGLE
INPUT
AMP
ATTENUATION
CORE
ZOUT = 75
8
ZIN (SINGLE) = 800
ZIN (DIFF) = 1.6k
R1
R2
VOUT
AD8327
DATEN
DATA
CLK
GND (5 PINS)
TXEN
SLEEP
VCC (5 PINS)
VIN+
VIN–
VERNIER
DECODE
DATA LATCH
SHIFT
REGISTER
POWER-DOWN
LOGIC
POWER
AMP
BYP
CXR
FEATURES
Supports DOCSIS Standard for Reverse Path
Transmission
Gain Programmable in 6.02 dB Steps over a 48.16 dB
Range
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
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
GENERAL DESCRIPTION
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
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
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.
FUNDAMENTAL FREQUENCY – MHz
–50
–60
–75
–65
–55
5
152535455565
DISTORTION
–
dBc
–70
HD3
HD2
VOUT = 60dBmV @ MAX GAIN
Figure 1. Harmonic Distortion vs. Frequency