Serial Digital Controlled
Variable Gain Line Driver
a
AD8320
FEATURES
8-Bit Serial Gain Control
FUNCTIO NAL BLO CK D IAGRAM
V/ V/ LSB Linear Gain Response
36 dB Gain Range
؎0.20 dB Gain Accuracy
VCC
GND
PWR AMP
AD8320
REFERENCE
Upper Bandw idth: 150 MHz
VOUT
22 dBm 1 dB Com pression Point (75 ⍀)
Drives Low Distortion Signals into 75 ⍀ Load:
–57 dBc SFDR at 42 MHz and 12 dBm Out
–46 dBc SFDR at 42 MHz and 18 dBm Out
Single Supply Operation from 5 V to 12 V
Maintains 75 ⍀ Output Im pedance
Pow er-Up and Pow er-Dow n Condition
Supports SPI Input Control Standard
VREF
VIN
REVERSE
AMP
INV.
BUF.
ATTENUATOR CORE
DATA LATCH
POWER-
DOWN/
SWITCH
INTER.
PD
DATA SHIFT REGISTER
APPLICATIONS
Coaxial Cable Driver
DATEN CLK
SDATA
HFC Cable Telephony System s
HFC High Speed Data Modem s
Interactive Set-Top Boxes
PC Plug-In Modem s
Interfaces w ith AD9853 I2C Controlled Digital Modulator
High Perform ance Digitally Controlled Variable Gain
Block
D ESCRIP TIO N
results in low glitch output during power-down and power-up
transitions, eliminating the need for an external switch.
T he AD8320 is a digitally controlled variable gain amplifier
optimized for coaxial line driving applications. An 8-bit serial
word determines the desired output gain over a 36 dB range
(256 gain levels). T he AD8320 provides linear gain response.
T he AD8320 is packaged in a 20-lead SOIC and operates from
a single +5 V through +12 V supply and has an operational
temperature range of –40°C to +85°C.
T he AD8320 is made up of a digitally controlled variable at-
tenuator of 0 dB to –36 dB, which is preceded by a low noise,
fixed gain buffer and followed by a low distortion high power
amplifier. T he AD8320 has a 220 Ω input impedance and ac-
cepts a single-ended input signal with a specified analog input
level of up to 0.310 V p-p. T he output is specified for driving a
75 Ω load, such as coaxial cable, although the AD8320 is ca-
pable of driving other loads. Distortion performance of –57 dBc
is achieved with an output level up to 12 dBm (3.1 V p-p) at
42 MHz, while –46 dBc distortion is achieved with an output
level up to 18 dBm (6.2 V p-p).
؊20
؊30
P
= 18dBm
O
؊40
؊50
؊60
P
= 12dBm
O
P
= 8dBm
O
A key performance and cost advantage of the AD8320 results
from the ability to maintain a constant 75 Ω output impedance
during power-up and power-down conditions. T his eliminates
the need for external 75 Ω back-termination, resulting in twice
the effective output voltage when compared to a standard opera-
tional amplifier. Additionally, the on-chip 75 Ω termination
؊70
؊80
P
= 4dBm
O
10
FREQUENCY – MHz
100
1
Figure 1. Worst Harm onic Distortion vs. Frequency for
Various Output Levels at VCC = 12 V
REV. 0
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reliable. However, no responsibility is assum ed by Analog Devices for its
use, nor for any infringem ents of patents or other rights of third parties
which m ay result from its use. No license is granted by im plication or
otherwise under any patent or patent rights of Analog Devices.
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© Analog Devices, Inc., 1998