SPT1019AIN Просмотр технического описания (PDF) - Signal Processing Technologies
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SPT1019AIN Datasheet PDF : 12 Pages
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Table II - Video Control Operation (Output values for setup = 10 IRE and 75 ohm standard load)
Sync
1
0
Blank
X
1
Ref
White
X
X
Bright
X
X
Data
Input
X
X
Out - (mA)
28.57
20.83
Out - (V)
-1.071
-0.781
Out - (IRE) Description
-40
Sync Level
0
Blank Level
0
0
1
1
X
0.00
0.000
110
Enhanced High Level
0
0
1
0
X
1.95
-0.073
100
Normal High Level
0
0
0
0
000...
19.40
-0.728
7.5
Normal Low Level
0
0
0
0
111...
1.95
-0.073
100
Normal High Level
0
0
0
1
000...
17.44
-0.654
17.5
Enhanced Low Level
0
0
0
1
111...
0.00
0.000
110
Enhanced High Level
DATA INPUTS AND VIDEO CONTROLS
The SPT1019 has standard single-ended data inputs. The
inputs are registered to produce the lowest differential data
propagation delay (skew) to minimize glitching. There are
also four video control inputs to generate composite video
outputs. These are Sync, Blank, Bright and Reference White
or Force High. Also provided is the Feedthrough control as
mentioned earlier. The controls and data inputs are all 10 KH
and 100K ECL compatible. In addition, all have internal
pulldown resistors to leave them at a logic low so the pins are
inactive when not used. This is useful if the devices are
applied as standard DACs without the need for video controls
or if less than eight bits are used.
The SPT1019 is usually configured in the synchronous
mode. In this mode, the controls and data are synchronized
to prevent pixel dropout. This reduces screen-edge distor-
tions and provides the lowest output noise while maintaining
the highest conversion rate. By leaving the Feedthrough (FT)
control open (low), each rising edge of the convert (CONV)
clock latches decoded data and control values into a D-type
internal register. The registered data is then converted into
the appropriate analog output by the switched current sinks.
When FT is tied high, the control inputs and data are not
registered. The analog output asynchronously tracks the
input data and video controls. Feedthrough itself is asynchro-
nous and usually used as a DC control.
The controls and data have to be present at the input pins for
a setup time of ts before, and a hold time of th after, the rising
edge of the clock (CONV) in order to be synchronously
registered. The setup and hold times are not important in the
asynchronous mode. The minimum pulse widths high (tPWH)
and low (tPWL) as well as settling time become the limiting
factors. (See figure 3.)
The video controls produce the output levels needed for
horizontal blanking, frame synchronization, etc., to be com-
patible with video system standards as described in
RS-343-A. Table II shows the video control effects on the
analog output. Internal logic governs Blank, Sync, and Force
High so that they override the data inputs as needed in video
applications. Sync overrides both the data and other controls
to produce full negative video output (figure 9).
Reference White video level output is provided by Force
High, which drives the internal digital data to full scale output
or 100 IRE units. Bright gives an additional 10% of full scale
value to the output level. This function can be used in graphic
displays for highlighting menus, cursors or warning mes-
sages. Again, if the devices are used in non-video applica-
tions, the video controls can be left open.
CONVERT CLOCK
For best performance, the clock should be ECL driven,
differentially, by utilizing CONV and CONV (figure 4). By
driving the clock this way, clock noise and power supply/
output intermodulation will be minimized. The rising edge of
the clock synchronizes the data and control inputs to the
SPT1019. Since the actual switching threshold of CONV is
determined by CONV, the clock can be driven single-ended
by connecting a bias voltage to CONV . The switching thresh-
old of CONV is set by this bias voltage.
ANALOG OUTPUTS
The SPT1019 has two analog outputs that are high imped-
ance, complementary current sinks. The outputs vary in
proportion to the input data, controls and reference current
values so that the full scale output can be changed by setting
ISet as mentioned earlier.
In video applications, the outputs can drive a doubly termi-
SPT
7
SPT1019
5/14/97
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