SPT1018

Table II - Video Control Operation (Output values for set-up = 10 IRE and 75 ohm standard load)

Sync

Blank

Ref

White

Bright

Data

Input

Out - (mA)

Out - (V)

Out - (IRE)

Description

1

X

X

X

X

28.57

-1.071

-40

Sync Level

0

1

X

X

X

20.83

-0.781

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

The SPT1018 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

edge of the clock (CONV) in order to be synchronously

registered. The set-up and hold times are not important in the

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,

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

determined by CONV, the clock can be driven single-ended

old of CONV is set by this bias voltage.

ANALOG OUTPUTS

The SPT1018 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

In video applications, the outputs can drive a doubly termi-

nated 50 or 75 ohm load to standard video levels. In the

standard configuration of figure 5, the output voltage is the

product of the output current and load impedance and is

between 0 and -1.07 V. The Out- output (figure 9) will provide

a video output waveform with the Sync pulse bottom at the

-1.07 V level. The Out+ is inverted with Sync up.

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