|
|
PDF AD8321 Data sheet ( Hoja de datos )
| Número de pieza | AD8321 | |
| Descripción | Gain Programmable CATV Line Driver | |
| Fabricantes | Analog Devices | |
| Logotipo |  |
|
Hay una vista previa y un enlace de descarga de AD8321 (archivo pdf) en la parte inferior de esta página. Total 20 Páginas | ||
|
No Preview Available !
a
FEATURES
Linear in dB Gain Response Over >53 dB Range
Drives Low Distortion >11 dBm Signal into 75 � Load:
–53 dBc SFDR at 42 MHz
Very Low Output Noise Level
Maintains Constant 75 � Output Impedance
Power-Up and Power-Down Condition
No Line Transformer Required
Upper Bandwidth: 235 MHz (Min Gain)
9 V Single Supply Operation
Power-Down Functionality
Supports SPI Interface
Low Cost
APPLICATIONS
Gain Programmable Line Driver
HFC High Speed Data Modems
Interactive CATV Set-Top Boxes
CATV Plant Test Equipment
General Purpose IF Variable Gain Block
Gain Programmable
CATV Line Driver
AD8321
FUNCTIONAL BLOCK DIAGRAM
VCC
GND
VIN+
VIN–
AD8321
INV ATTENUATOR CORE
PWR
AMP
REVERSE
AMP
VOUT
DATADASTHAIFLTARTECGHISTER
DATA SHIFT REGISTER
POWER-
DOWN/
SWITCH
INTER
PD
DATEN CLK
SDATA
DESCRIPTION
The AD8321 is a low cost digitally controlled variable gain
amplifier optimized for coaxial line driving applications such as
cable modems that are designed to the DOCSIS* (upstream)
standard. An 8-bit serial word determines the desired output gain
over a 53.4 dB range, resulting in gain changes of 0.75 dB/LSB.
The AD8321 comprises a digitally controlled variable attenuator
of 0 dB to –53.4 dB, which is preceded by a low noise, fixed
gain buffer and followed by a low distortion high power ampli
fier. The AD8321 accepts a differential or single-ended input
signal. The output is specified for driving a 75 W load, such as
coaxial cable, although the AD8321 is capable of driving other
loads. Performance of –53 dBc is achieved with an output level
up to 11 dBm at 42 MHz bandwidth using a 9 V supply.
A key performance and cost advantage of the AD8321 results
from the ability to maintain a constant 75 W output impedance
during power-up and power-down conditions. This eliminates
the need for external 75 W termination, resulting in twice the
effective output voltage when compared to a standard opera
tional amplifier, thus eliminating the need for a transformer.
*Data-Over-Cable Service Interface Specifications
The AD8321 is packaged in a low cost 20-lead SOIC, operates
from a single +9 V supply, and has an operational temperature
range of –40∞C to +85∞C.
–40
fO = 42MHz
VIN = 137mV p-p
(PIN = –15dBm)
–50 (POUT = 11dBm @
MAX GAIN)
–60
HD3
–70
HD2
–80
–90
0
8 16 24 32 40 48 56 64 72
GAIN CONTROL – Decimal
Figure 1. Harmonic Distortion vs. Gain Control
REV. A
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 that
may result from its use. No license is granted by implication or otherwise
under any patent or patent rights of Analog Devices. Trademarks and
registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
www.analog.com
Fax: 781/461-3113 © 2005 Analog Devices, Inc. All rights reserved.
1 page  
0.6
0.3
0
–0.3
f = 10MHz
f = 42MHz
–0.6
–0.9
f = 65MHz
–1.2 0
8 16 24 32 40 48 56 64 72
GAIN CONTROL – Decimal
Figure 4. Gain Error vs. Gain Control
Typical Performance Characteristics–AD8321
30
20 71D
10
0 46D
–10
23D
–20
–30
00D
–40
0.1
1 10 100
FREQUENCY – MHz
Figure 5. AC Response
1000
70
f = 10MHz
PD =1
60
50
40
30
20
10
0 8 16 24 32 40 48 56 64 72
GAIN CONTROL – Decimal
Figure 6. Output Referred Noise vs.
Gain Control
70
60
MAX GAIN
(71D)
50
PD = 1
40
30
MIN GAIN
(00D)
20
10
1 10 100
FREQUENCY – MHz
Figure 7. Output Referred Noise vs.
Frequency
–30
fO = 65MHz
VIN = 0.137V p-p
–40 (PIN = –15dBm)
(POUT = 11dBm @
MAX GAIN)
–50
HD3
–60
HD2
–70
–80 0
8 16 24 32 40 48 56 64 72
GAIN CONTROL – Decimal
Figure 8. Harmonic Distortion vs.
Gain Control
–47
PIN = –14dBm
(POUT = 12dBm @
MAX GAIN)
–50
PIN = –13dBm
(POUT = 13dBm @
MAX GAIN)
–53
PIN = –15dBm
(POUT = 11dBm @
MAX GAIN)
–56
–59
5
PIN = –17dBm
(POUT = 9dBm @
MAX GAIN)
15 25 35 45 55 65
FUNDAMENTAL FREQUENCY – MHz
Figure 9. Second Order Harmonic
Distortion vs. Frequency for Various
Input Levels
–47
PIN = –13dBm
(POUT = 13dBm @
MAX GAIN)
–50
PIN = –14dBm
(POUT = 12dBm @
MAX GAIN)
–53
–56
–59
5
PIN = –15dBm
(POUT = 11dBm @
MAX GAIN)
PIN = –17dBm
(POUT = 9dBm @
MAX GAIN)
15 25 35 45 55 65
FUNDAMENTAL FREQUENCY – MHz
Figure 10. Third Order Harmonic
Distortion vs. Frequency for Various
Input Levels
20
POUT = 11dBm
MAX GAIN
0
–20
–40
–60
–80
41.0
41.4 41.8 42.2 42.6
FREQUENCY – MHz
43.0
Figure 11. Two-Tone Intermodula-
tion Distortion
30
29
POUT = 11dBm
MAX GAIN
28
27
26
25
24
23
22
5
15 25 35 45 55
FREQUENCY – MHz
65
Figure 12. Third Order Intercept vs.
Frequency
REV. A
–5–
5 Page 
AD8321
Distortion and DOCSIS
Care must be taken when selecting attenuation levels specified
in Table I as the output signal from the AD8321 must compen
sate for the losses resulting from any added attenuation as well
as the insertion losses associated with the diplexer. An increase
in input signal becomes apparent at the upper end of the gain
range and will be needed to achieve the 58 dBmV at the modem
output. The insertion losses of the diplexer may vary, depend
ing on the quality of the diplexer and whether the frequency of
operation is in near proximity to the cut-off frequency of the
low-pass filter. Figures 9 and 10 show the expected second
and third harmonic distortion performance vs. fundamental
frequency at various input power levels. These graphs indicate
the worst harmonic levels exhibited over the entire output range
of the AD8321 (i.e., –27 dB to +26 dB). Figures 9 and 10 are
useful when it is necessary to determine inband harmonic levels
(5 MHz to 42 MHz or 5 MHz to 65 MHz). Harmonics that
are higher in frequency, as compared to the cutoff frequency of
the low-pass filter of the diplexer, will be further suppressed by
the stop band attenuation level of the LP filter in the diplexer.
Designers must balance the need to improve noise performance
by adding attenuation with the resulting need for increased
signal amplitude while maintaining DOCSIS specified dis
tortion performance.
Evaluation Board Features and Operation
The AD8321 evaluation board (p/n AD8321-EVAL) and com
panion software program written in Microsoft Visual Basic are
available through Analog Devices, Inc. and can be used to
control the AD8321 Variable Gain Upstream Power Amplifier
via the parallel port of a PC. This evaluation package provides a
convenient way to program the gain/attenuation of the AD8321
without the addition of any external glue logic. AD8321-EVAL
has been developed to facilitate the use of the AD8321 in an
application targeted at DOCSIS compliance. A low cost Alpha
Industries AS128-73 GaAs 2 Watt High Linearity SPDT RF
switch (referred to as SWb) is included on the evaluation board
(see Figure 28) along with accommodations for a user specified
75 W matching attenuator (See Table I for a table of resistor
values of attenuators ranging from –1 dB to –4 dB). The
AD8321 DATEN, CLK and SDATA digital lines are pro
grammed according to the gain setting and mode of operation
selected using the Windows® interface of the control software
(see Figure 30). The serial interface of the AD8321 is ad
dressed through the parallel port of a PC using four or more
bits (plus ground). Two additional bits from the parallel port
are used to control the RF switch(s). This software programs
the AD8321 gain or attenuation, incorporates asynchronous
control of the power-down feature (PD Pin 6) as well as asyn
chronous control of the Alpha Industries RF switch(es) AS128
73.* A standard printer cable is used to feed the necessary data
to the AD8321-EVAL board. These features allow the designer
to fully develop and evaluate the upstream signal path begin
ning at the input to the PA.
Windows is a registered trademark of Microsoft Corporation.
*Alpha Industries @ www.alphaind.com
Overshoot on PC Printer Ports
The data lines on some PC parallel printer ports have excessive
overshoot. Overshoot presented to the CLK pin (TP7 on the
evaluation board) may cause communications problems. The
evaluation board layout was designed to accommodate a series
resistor and shunt capacitor (R6 and C12) if required to filter or
condition the CLK data.
Between Burst Transient Reduction
In order to reduce the amplitude of the “Burst On/Off Tran
sient” glitch at the output of the AD8321, when switching from
forward transmit mode to reverse powered down mode, position
the SWb switch in Figure 28 to position “a” before changing the
logic applied to PD Pin 6 of the AD8321 from Logic 1-to-0
(and also 0-to-1). Use the “Enable Output Switch” feature in
the evaluation board control software (see Figure 31) to select
the appropriate position of the AS128-73 switch. A check in this
box enables the switch to pass upstream data to the output of the
evaluation board. The AS128-73 produces a glitch of approxi
mately 5 mV p-p regardless of the AD8321 gain setting. The
AD8321-EVAL board comes with resistors and capacitors
installed on the logic lines controlling the RF switch (R8, R9,
C16, C17). These values were selected to reduce the glitch
amplitude to DOCSIS acceptable levels and may be modified
if required. The SPDT function of the AS128-73 RF switch
accommodates the need to maintain proper termination when
the diplexer is disconnected from the output of the AD8321.
The AD8321-EVAL board accommodates the needed back
termination (refer to the Cb and Rb of the evaluation circuit).
Differential Inputs
When evaluating the AD8321 in differential input mode, termi
nation resistor(s) should be selected and applied such that the
combined resistance of the termination resistor(s) and the input
impedance of the AD8321 results in a match between the signal
source impedance and the input impedance of the AD8321. The
evaluation board is designed to accommodate Mini-Circuits T1
6T-KK81 1:1 transformer for the purposes of converting a
single-ended (i.e., ground referenced) input signal to differen
tial inputs. The following paragraphs identify three options for
providing differential input signals to the AD8321 evaluation
board. Option 1 uses a transformer to produce a truly differen
tial input signal. The termination resistor(s) specified in Option
1 and 2 may also be used without the transformer if a differen
tial signal source is available. Option 2 uses a transformer and-
produces ground referenced input signals that are separated in
phase by 180∞. Option 3 relies on differential signals provided
by the user and does not employ a transformer for single-to
differential conversion.
Differential Input Option 1: Install the Mini-Circuits T1-6T
KK81 1:1 transformer in the T1 location of the evaluation
board. Jumpers J1, J2 and J3 should be applied pointing in the
direction of the transformer. A differential input termination
resistor of 82.5 W can be used in the R3 position. This value
should be used when the single-ended input signal has a source
impedance of 75 W. In this configuration, the input signal must
be applied to the VIN+/DIFF IN port of the evaluation board.
An open circuit is required in R1, R2 and J4 positions resulting
in a 75 W differential input termination to the AD8321. If a
50 W single-ended input source is applied to the VIN+/DIFF IN
port, the R3 value should be 53.6 W.
REV. A
–11–
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet AD8321.PDF ] | |
Hoja de datos destacado
| Número de pieza | Descripción | Fabricantes |
| AD8320 | Serial Digital Controlled Variable Gain Line Driver | Analog Devices |
| AD8321 | Gain Programmable CATV Line Driver | Analog Devices |
| AD8322 | 5 V CATV Line Driver Coarse Step Output Power Control | Analog Devices |
| AD8323 | 5 V CATV Line Driver Fine Step Output Power Control | Analog Devices |
| Número de pieza | Descripción | Fabricantes |
| SLA6805M | High Voltage 3 phase Motor Driver IC. |
 Sanken |
| SDC1742 | 12- and 14-Bit Hybrid Synchro / Resolver-to-Digital Converters. |
Analog Devices |
|
DataSheet.es es una pagina web que funciona como un repositorio de manuales o hoja de datos de muchos de los productos más populares, |
| DataSheet.es | 2020 | Privacy Policy | Contacto | Buscar |