SPT1018

Figure 1 - Functional Diagram

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.

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Decoding

Logic

Data

Registers

Current

Sources

And

Switches

Current

Source

Biasing

Amp

+-

Out +

Out -

8

Composite

Video Controls

Feedthrough

D0 - D7

2

CONV

CONV

Ref+

VEE

VCC

Ref-

Table I - The SPT1018 Family and Speed Designations

PART NUMBER

UPDATE

COMMENTS

SPT1018A

275 MWPS

Suitable for 1200 X 1500 to 1500 X 1800

displays at 60 to 90 Hz update rate.

SPT1018B

165 MWPS

Suitable for 1024 X 1280 to 1200 X 1500

displays at 60 to 90 Hz update rate.

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5/14/97