AD8322 Datasheet, PDF (1/16 Pages) Analog Devices – 5 V CATV Line Driver Coarse Step Output Power Control

a
5 V CATV Line Driver
Coarse Step Output Power Control
AD8322
FEATURES
Supports DOCSIS Standard for Reverse Path
Transmission
Gain Programmable in 6 dB Steps Over a 42 dB
Range
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
5 V Supply Operation
Supports SPI Interfaces
APPLICATIONS
Gain Programmable Line Driver
DOCSIS-Compliant Data Modems
Interactive Set-Top Boxes
PC Plug-in Modems
General-Purpose Digitally Controlled Variable Gain Block
FUNCTIONAL BLOCK DIAGRAM
V_CC (7 PINS)
R1
AD8322
V_IN+
V_IN–
DIFF
OR SINGLE
INPUT
AMP
BUFFER
R2
Z_IN (SINGLE) = 210⍀
Z_IN (DIFF) = 235⍀
ATTENUATION
CORE
8
DECODE
8
DATA LATCH
POWER
AMP
Z_OUT DIFF =
75⍀
POWER-DOWN
LOGIC
V_OUT+
V_OUT–
8
SHIFT
REGISTER
DATEN DATA CLK
GND (12 PINS)
PD
GENERAL DESCRIPTION
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.
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.
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.
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.
–55
f_O = 42MHz
V_O = 60dBmV
@ MAX GAIN
–60
HD3
–65
HD2
–70
–75
1
2
4
8
16
32
64
128
GAIN CODE – Decimal
Figure 1. Harmonic Distortion vs. Gain Control
REV. 0
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