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ADV7128 Schematic ( PDF Datasheet ) - Analog Devices

Teilenummer ADV7128
Beschreibung CMOS 80 MHz/ 10-Bit Video DAC
Hersteller Analog Devices
Logo Analog Devices Logo 




Gesamt 8 Seiten
ADV7128 Datasheet, Funktion
a
CMOS
80 MHz, 10-Bit Video DAC
FEATURES
80 MHz Pipelined Operation
10-Bit D/A Converters
RS-343A/RS-170 Compatible Outputs
TTL Compatible Inputs
+5 V CMOS Monolithic Construction
28-Pin SOIC Package
APPLICATIONS
High Definition Television (HDTV)
High Resolution Color Graphics
Digital Radio Modulation
CAE/CAD/CAM Applications
Image Processing
Instrumentation
Video Signal Reconstruction
Direct Digital Synthesis (DDS) & I/O Modulation
Wireless LAN
Wireless Local Loop
SPEED GRADES
80 MHz
50 MHz
30 MHz
CLOCK
ADV7128
FUNCTIONAL BLOCK DIAGRAM
FS
VAA ADJUST VREF
ADV7128
REFERENCE
AMPLIFIER
COMP
D0
10
DATA
10
REGISTER
DAC
IOUT
D9
GND
GENERAL DESCRIPTION
The ADV7128 (ADV®) is a video speed, digital-to-analog con-
verter on a single monolithic chip. It consists of a high speed,
10-bit, video D/A converters; a standard TTL input interface;
and a high impedance, analog output, current source.
The ADV7128 has a 10-bit pixel input port. A single +5 V
power supply, an external 1.23 V reference and pixel clock input
are and all that are required to make the part operational.
The ADV7128 is capable of generating video output signals
which are compatible with RS-343A, RS-170 and most pro-
posed production system HDTV video standards, including
SMPTE 240M.
The ADV7128 is fabricated in a +5 V CMOS process. Its
monolithic CMOS construction ensures greater functionality
with low power dissipation. The ADV7128 is available in a 28-
lead small outline IC (SOIC).
PRODUCT HIGHLIGHTS
1. Fast video refresh rate, 80 MHz.
2. Guaranteed monotonic to 10 bits. Ten bits of resolution al-
lows for implementation of linearization functions such as
gamma correction and contrast enhancement.
3. Compatible with a wide variety of high resolution color
graphics systems including RS-343A/RS-170 and the pro-
posed SMPTE 240M standard for HDTV.
4. Combined with a numerically controlled oscillator (AD9955),
it forms a complete frequency synthesizer (DDS).
5. Using the parts reduced power output DAC modes, it is
ideal for power and cost sensitive communications type
applications.
ADV is a registered trademark of Analog Devices, Inc.
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: 617/329-4700
Fax: 617/326-8703






ADV7128 Datasheet, Funktion
ADV7128
Reference Input
An external 1.23 V voltage reference is required to drive the
ADV7128. The AD589 from Analog Devices is an ideal choice
of reference. It is a two-terminal, low cost, temperature com-
pensated bandgap voltage reference which provides a fixed
1.23 V output voltage for input currents between 50 µA and
5 mA. Figure 4 shows a typical reference circuit connection dia-
gram. The voltage reference gets its current drive from the
ADV7128’s VAA through an on-board 1 kresistor to the VREF
pin. A 0.1 µF ceramic capacitor is required between the COMP
pin and VAA. This is necessary so as to provide compensation for
the internal reference amplifier.
A resistance RSET connected between RSET and GND deter-
mines the amplitude of the output video level according to the
following equation:
IOUT (mA) = 7,969 × VREF(V)/RSET()
(1)
Using a variable value of RSET, as shown in Figure 4, allows for
accurate adjustment of the analog output video levels. Use of a
fixed 560 RSET resistor yields the analog output levels as
quoted in the specification page. These values typically corre-
spond to the RS-343A video waveform values as shown in
Figure 3.
COMP
ANALOG POWER PLANE
0.01µF
+5V
VAA
TO DAC
1k
VREF
RSET
I REF ~ 5mA
ADV7128
R SET
560
GND
500
100
AD589
(1.235V
VOLTAGE
REFERENCE)
*ADDITIONAL CIRCUITRY, INCLUDING DECOUPLING COMPONENTS,
EXCLUDED FOR CLARITY
Figure 4. Reference Circuit
D/A Converter
The ADV7128 contains a 10-bit D/A converter. The DAC is
designed using an advanced, high speed, segmented architec-
ture. The bit currents corresponding to each digital input are
routed to either the analog output (bit = “1”) or GND (bit =
“0”) by a sophisticated decoding scheme. The use of identical
current sources in a monolithic design guarantees monotonicity
and low glitch. The on-board operational amplifier stabilizes the
full-scale output current against temperature and power supply
variations.
Analog Output
The analog output of the ADV7128 is a high impedance current
source. The current output is capable of directly driving a
37.5 load, such as a doubly terminated 75 coaxial cable.
Figure 5a shows the required configuration for the output con-
nected into a doubly terminated 75 load. This arrangement
will develop RS-343A video output voltage levels across a 75
monitor.
DAC
IOUT
ZS = 75
(SOURCE
TERMINATION)
ZO = 75
(CABLE)
ZL= 75
(MONITOR)
Figure 5a. Analog Output Termination for RS-343A
A suggested method of driving RS-170 video levels into a 75
monitor is shown in Figure 5b. The output current level of the
DAC remains unchanged, but the source termination resistance,
ZS, on the DAC is increased from 75 to 150 .
DAC
IOUT
ZO = 75
(CABLE)
ZS = 150
(SOURCE
TERMINATION)
ZL= 75
(MONITOR)
Figure 5b. Analog Output Termination for RS-170
More detailed information regarding load terminations for vari-
ous output configurations, including RS-343A and RS-170, is
available in an Application Note entitled “Video Formats & Re-
quired Load Terminations” available from Analog Devices,
publication no. E1228-15-1/89.
Figure 3 shows the video waveforms associated with the current
output driving the doubly terminated 75 load of Figure 5a.
Gray Scale Operation
The ADV7128 can be used for stand-alone, gray scale (mono-
chrome) or composite video applications (i.e., only one channel
used for video information).
Video Output Buffer
The ADV7128 is specified to drive transmission line loads,
which is what most monitors are rated as. The analog output
configurations to drive such loads are described in the Analog
Interface section and illustrated in Figure 5. However, in some
applications it may be required to drive long “transmission line”
cable lengths. Cable lengths greater than 10 meters can attenu-
ate and distort high frequency analog output pulses. The inclu-
sion of output buffers will compensate for some cable distortion.
Buffers with large full power bandwidths and gains between 2
and 4 will be required. These buffers will also need to be able to
supply sufficient current over the complete output voltage
swing. Analog Devices produces a range of suitable op amps for
such applications. These include the AD84x series of monolithic
op amps. In very high frequency applications (80 MHz), the
AD9617 is recommended. More information on line driver buff-
ering circuits is given in the relevant op amp data sheets.
Use of buffer amplifiers also allows implementation of other
video standards besides RS-343A and RS-170. Altering the gain
components of the buffer circuit will result in any desired
video level.
–6– REV. 0

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