AD8323_15 Datasheet, PDF (1/16 Pages) Analog Devices – 5 V CATV Line Driver Fine Step Output Power Control

a
5 V CATV Line Driver Fine Step
Output Power Control
AD8323
FEATURES
FUNCTIONAL BLOCK DIAGRAM
Supports DOCSIS Standard for Reverse Path
Transmission
V_CC (7 PINS)
BYP
Gain Programmable in 0.75 dB Steps Over a 53.5 dB
Range
R1
AD8323
Low Distortion at 60 dBmV Output
V_IN+
V_OUT+
–56 dBc SFDR at 21 MHz
DIFF OR
SINGLE
BUFFER
ATTENUATION
POWER
–55 dBc SFDR at 42 MHz
Output Noise Level
–48 dBmV in 160 kHz
Maintains 75 ⍀ Output Impedance
Power-Up and Power-Down Condition
Upper Bandwidth: 100 MHz (Full Gain Range)
E _{5 V Supply Operation}
Supports SPI Interfaces
APPLICATIONS
T Gain-Programmable Line Driver
HFC High-Speed Data Modems
Interactive Set-Top Boxes
PC Plug-in Modems
E _{General-Purpose Digitally Controlled Variable Gain Block}
V_IN–
INPUT
AMP
R2
Z_IN (SINGLE) = 800⍀
Z_IN (DIFF) = 1.6k⍀
CORE
8
DECODE
AMP
Z_OUT DIFF =
75⍀
V_OUT–
8
DATA LATCH
POWER-DOWN
LOGIC
8
SHIFT
REGISTER
DATEN DATA CLK GND (11 PINS) PD
SLEEP
L ^{GENERAL DESCRIPTION}
The AD8323 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
O _{over a 53.5 dB range resulting in gain changes of 0.7526 dB/LSB.}
The AD8323 comprises a digitally controlled variable attenuator
of 0 dB to –53.5 dB, which is preceded by a low noise, fixed
gain buffer and is followed by a low distortion high power am-
S _{plifier. The AD8323 accepts a differential or single-ended input}
signal. The output is specified for driving a 75 Ω load, such as
coaxial cable.
B ^{Distortion performance of –56 dBc is achieved with an output}
level up to 60 dBmV at 21 MHz bandwidth. A key performance
and cost advantage of the AD8323 results from the ability to main-
tain a constant 75 Ω output impedance during power-up and
O ^{power-down conditions. This eliminates the need for external 75 Ω}
–50
F_O = 42MHz
P_O = 60dBmV @ MAX GAIN
–55
–60
HD3
–65
HD2
–70
–75
0
8 16 24 32 40 48 56 64 72
GAIN CONTROL – DEC Code
Figure 1. Harmonic Distortion vs. Gain Control
termination, resulting in twice the effective output voltage when
compared to a standard operational amplifier. In addition, this
device has a sleep mode function that reduces the quiescent
current to 4 mA.
The AD8323 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
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