Figure 1 - Functional Diagram
D0 - D7
8
Composite
Video Controls
CONV
CONV
Feedthrough
2
Decoding
Logic
Data
Registers
Current
Sources
And
Switches
Out +
Out -
4
Current
Source
Biasing
Amp
+
-
VEE
VCC
Ref+
Ref-
APPLICATION INFORMATION
The SPT1018 is a high speed video digital-to-analog con-
verter capable of conversion rates of up to 275 MWPS. This
makes the device suitable for driving 1500 X 1800 pixel
displays at 70 to 90 Hz update rates.
The SPT1018 is separated into different conversion rate
categories as shown in table I.
The SPT1018 has 10 KH and 100K ECL logic level compat-
ible video controls and data inputs. The complementary
analog output currents produced by the devices are propor-
tional to the product of the digital control and data inputs in
conjunction with the analog reference current. The SPT1018
is segmented so that the four MSBs of the input data are
separated into a parallel thermometer code. From here,
fifteen identical current sinks are driven to fabricate sixteen
coarse output levels. The remaining four LSBs drive four
binary weighted current switches.
The MSB currents are then summed with the LSBs, which
provide a one-sixteenth of full scale contribution, to provide
the 256 distinct analog output levels.
The video control inputs drive weighted current sinks that are
added to the output current to produce composite video
output levels. These controls, Sync, Blank, Reference White
(Force High), and Bright are needed in video applications.
Another feature that similar video D/A converters do not have
is the Feedthrough Control. This pin allows registered or
unregistered operation of the video control and data inputs.
In the registered mode, the composite functions are latched
to the pixel data to prevent screen-edge distortions generally
found on unregistered video DACs.
Table I - The SPT1018 Family and Speed Designations
PART NUMBER
SPT1018A
UPDATE
275 MWPS
COMMENTS
Suitable for 1200 X 1500 to 1500 X 1800
displays at 60 to 90 Hz update rate.
Suitable for 1024 X 1280 to 1200 X 1500
displays at 60 to 90 Hz update rate.
SPT1018B
165 MWPS
SPT1018
4
5/14/97
CADEKA [ CADEKA MICROCIRCUITS LLC. ]
