adv101 Analog Devices, Inc., adv101 Datasheet - Page 8

• Manufacturer Part Number: adv101
• Description: Cmos 80 Mhz, Triple 8-bit Video Dac
• Manufacturer: Analog Devices, Inc.

ADV101
A resistance R
determines the amplitude of the output video level according to
the following equations:
If SYNC is not being encoded onto the green channel, then
Equation 1 will be similar to Equation 2.
Using a variable value of R
accurate adjustment of the analog output video levels. Use of a
fixed 560
quoted in the specification page. These values also correspond
to the RS-343A video waveform values as shown in Figure 3.
D/A Converters
The ADV101 contains three matched 8-bit D/A converters. The
DACs are designed using an advanced, high speed, segmented
architecture. The bit currents corresponding to each digital in-
put are routed to either the analog output (bit = “1”) or GND
(bit = “0”) by a sophisticated decoding scheme. As all this cir-
cuitry is on one monolithic device, matching between the three
DACs is optimized. As well as matching, the use of identical
current sources in a monolithic design guarantees monotonicity
and low glitch. The onboard operational amplifier stabilizes the
full-scale output current against temperature and power supply
variations.
Analog Outputs
The ADV101 has three analog outputs, corresponding to the
red, green and blue video signals. A fourth analog output
(I
zation information onto the green signal. In this case, I
connected to IOG. (See “Video Synchronization and Control”
section.)
The red, green and blue analog outputs of the ADV101 are high
impedance current sources. Each one of these three RGB cur-
rent outputs is capable of directly driving a 37.5
a doubly terminated 75
*ADDITIONAL CIRCUITRY, INCLUDING
DECOUPLING COMPONENTS,
EXCLUDED FOR CLARITY
SYNC
TO DACs
) can be used if it is required to encode video synchroni-
IOG (mA) = 12,082
IOR, IOB (mA) = 8,628
COMP
ADV101*
R
SET
SET
0.1 F
ANALOG POWER PLANE
Figure 4. Reference Circuit
resistor yields the analog output levels as
connected between FS ADJUST and GND
SET
coaxial cable. Figure 5a shows the
V
V
V
1k
FS ADJUST
GND
, as shown in Figure 4, allows for
AA
REF
REF
560
R
V
SET
(V)/R
REF
+
(V)/R
5V
500
100
SET
I
( )
REF
SET
~ ~
4mA
( )
load, such as
AD589
(1.235V
VOLTAGE
REFERENCE)
SYNC
is
(1)
(2)
–8–
required configuration for each of the three RGB outputs con-
nected into a doubly terminated 75
will develop RS-343A video output voltage levels across a 75
monitor.
A suggested method of driving RS-170 video levels into a 75
monitor is shown in Figure 5b. The output current levels of the
DACs remain unchanged, but the source termination resistance,
Z
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 &
Required Load Terminations” available from Analog Devices,
publication number E1228-15-1/89.
Figure 3 shows the video waveforms associated with the three
RGB outputs driving the doubly terminated 75
5a. As well as the gray scale levels, black level to white level, the
diagram also shows the contributions of SYNC and BLANK.
These control inputs add appropriately weighted currents to the
analog outputs, producing the specific output level requirements
for video applications. Table I details how the SYNC and
BLANK inputs modify the output levels.
Gray Scale Operation
The ADV101 can be used for stand-alone, gray scale (mono-
chrome) or composite video applications (i.e., only one channel
used for video information). Any one of the three channels, red,
green or blue can be used to input the digital video data. The
two unused video data channels should be tied to logical zero.
S
, on each of the three DACs is increased from 75
Figure 5a. Analog Output Termination for RS-343A
Figure 5b. Analog Output Termination for RS-170
TERMINATION REPEATED THREE TIMES
FOR RED, GREEN AND BLUE DACs
TERMINATION REPEATED THREE TIMES
FOR RED, GREEN AND BLUE DACs
DACs
DACs
TERMINATION)
TERMINATION)
Z = 150
S
(SOURCE
(SOURCE
Z = 75
S
IOR, IOG, IOB
IOR, IOG, IOB
Z = 75
Z = 75
(CABLE)
(CABLE)
O
O
load. This arrangement
load of Figure
Z = 75
(MONITOR)
Z = 75
(MONITOR)
L
L
to 150 .
REV. B