a
FEATURES
8-Bit Serial Gain Control
V/V/LSB Linear Gain Response
36 dB Gain Range
0.20 dB Gain Accuracy
Upper Bandwidth: 150 MHz
22 dBm 1 dB Compression 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 Impedance
Power-Up and Power-Down Condition
Supports SPI Input Control Standard
APPLICATIONS
Coaxial Cable Driver
HFC Cable Telephony Systems
HFC High Speed Data Modems
Interactive Set-Top Boxes
PC Plug-In Modems
Interfaces with AD9853 I
2
C Controlled Digital Modulator
High Performance Digitally Controlled Variable Gain
Block
Serial Digital Controlled
Variable Gain Line Driver
AD8320
FUNCTIONAL BLOCK DIAGRAM
VCC
GND
PWR AMP
REFERENCE
AD8320
VOUT
VREF
VIN
INV.
ATTENUATOR CORE
REVERSE
AMP
BUF.
DATA LATCH
POWER-
DOWN/
SWITCH
INTER.
PD
DATA SHIFT REGISTER
DATEN
CLK
SDATA
DESCRIPTION
The 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). The AD8320 provides linear gain response.
The 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. The 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. The 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).
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. This 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
results in low glitch output during power-down and power-up
transitions, eliminating the need for an external switch.
The 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.
20
30
P
O
= 18dBm
DISTORTION – dBc
40
50
P
O
= 8dBm
60
P
O
= 12dBm
70
P
O
= 4dBm
80
1
10
FREQUENCY – MHz
100
Figure 1. Worst Harmonic Distortion vs. Frequency for
Various Output Levels at V
CC
= 12 V
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
World Wide Web Site: http://www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 1998
AD [ ANALOG DEVICES ]
