5 V CATV Line Driver
Coarse Step Output Power Control
a
AD8322
FEATURES
FUNCTIONAL BLOCK DIAGRAM
Supports DOCSIS Standard for Reverse Path
Transmission
V
(7 PINS)
CC
Gain Programmable in 6 dB Steps Over a 42 dB
Range
R1
AD8322
Low Distortion at 60 dBmV Output
–58 dBc SFDR at 21 MHz
–56 dBc SFDR at 42 MHz
Output Noise Level
–46 dBmV in 160 kHz Bandwidth
Maintains 75 ⍀ Output Impedance
Power-Up and Power-Down Condition
180 MHz Bandwidth
V
V
OUT+
IN+
DIFF
ATTENUATION
OR SINGLE
INPUT
BUFFER
POWER
AMP
CORE
V
V
OUT–
IN–
AMP
8
Z
DIFF =
OUT
75⍀
DECODE
R2
POWER-DOWN
LOGIC
Z
Z
(SINGLE) = 210⍀
(DIFF) = 235⍀
IN
IN
8
DATA LATCH
8
SHIFT
REGISTER
5 V Supply Operation
Supports SPI Interfaces
DATEN DATA CLK
GND (12 PINS)
PD
APPLICATIONS
Gain Programmable Line Driver
DOCSIS-Compliant Data Modems
Interactive Set-Top Boxes
PC Plug-in Modems
General-Purpose Digitally Controlled Variable Gain Block
–55
–60
GENERAL DESCRIPTION
f
V
= 42MHz
O
The AD8322 is a low-cost, digitally controlled variable gain ampli-
fier 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 42.14 dB range, with gain steps of 6.02 dB/major
carry.
= 60dBmV
O
@ MAX GAIN
HD3
HD2
–65
–70
The AD8322 comprises a digitally controlled variable attenuator
of 0 dB to –42.14 dB, which is preceded by a low-noise, fixed-gain
buffer and is followed by a low-distortion, high-power ampli-
fier. The AD8322 accepts a differential or single-ended input
signal. The output is specified for driving a 75 Ω load, such as
coaxial cable.
–75
1
2
4
8
16
32
64
128
Distortion performance of –58 dBc is achieved with an output level
up to 60 dBmV at 21 MHz bandwidth. A key performance and
cost advantage of the AD8322 results from the ability to maintain
a constant 75 Ω output impedance during power-up and power-
down conditions. This eliminates the need for external 75 Ω
termination resulting in twice the effective output voltage when
compared to a standard operational amplifier.
GAIN CODE – Decimal
Figure 1. Harmonic Distortion vs. Gain Control
The AD8322 is packaged in a low-cost 28-lead TSSOP, operates
from a single 5 V supply, and has an operational temperature
range of –40°C to +85°C.
REV. 0
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
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
Fax: 781/326-8703
World Wide Web Site: http://www.analog.com
© Analog Devices, Inc., 2000
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