ADV7120

REV. B

–7–

If we, therefore, have a graphics system with a 1024

× 1024

resolution, a noninterlaced 60 Hz refresh rate and a retrace fac-

tor of 0.8, then:

Dot Rate = 1024

× 1024 × 60/0.8

= 78.6 MHz

The required CLOCK frequency is thus 78.6 MHz.

All video data and control inputs are latched into the ADV7120

on the rising edge of CLOCK, as previously described in the

“Digital Inputs” section. It is recommended that the CLOCK

input to the ADV7120 be driven by a TTL buffer (e.g.,

74F244).

92.5 IRE

7.5 IRE

40 IRE

WHITE LEVEL

BLACK LEVEL

BLANK LEVEL

SYNC LEVEL

19.05

0.714

26.67

1.000

1.44

0.054

9.05

0.340

0

0

7.62

0.286

0

0

mA

V

mA

V

RED, BLUE

GREEN

NOTES

1. OUTPUTS CONNECTED TO A DOUBLY TERMINATED 75

Ω LOAD.

2. V

3. RS-343A LEVELS AND TOLERANCES ASSUMED ON ALL LEVELS.

Figure 3. RGB Video Output Waveform

Video Synchronization and Control

The ADV7120 has a single composite video sync (SYNC) input

control. Many graphics processors and CRT controllers have

the ability of generating horizontal sync (HSYNC), vertical sync

(VSYNC) and composite SYNC.

In a graphics system which does not automatically generate a

composite SYNC signal, the inclusion of some additional logic

circuitry will enable the generation of a composite SYNC signal.

IOG output, thus encoding video synchronization information

onto the green video channel. If it is not required to encode sync

information onto the ADV7120’s analog outputs, the SYNC in-

nected to analog ground.

Reference Input

An external 1.23 V voltage reference is required to drive

the ADV7120. The AD589 from Analog Devices is an

ideal choice of reference. It is a two-terminal, low cost,

temperature compensated bandgap voltage reference which

provides a fixed 1.23 V output voltage for input currents

between 50

µA and 5 mA. Figure 4 shows a typical refer-

ence circuit connection diagram. The voltage reference gets

board 1 k

Ω resistor to the V

µF ceramic ca-

This is necessary so as to provide compensation for the

internal reference amplifier.

Table I. Video Output Truth Table

IOG

IOR, IOB

REF

DAC

Description

(mA)

l

(mA)

WHITE

SYNC

BLANK

Input Data

WHITE LEVEL

26.67

19.05

1

1

1

xxH

WHITE LEVEL

26.67

19.05

0

1

1

FFH

VIDEO

video + 9.05

video + 1.44

0

1

1

data

VIDEO to BLANK

video + 1.44

video + 1.44

0

0

1

data

BLACK LEVEL

9.05

1.44

0

1

1

00H

BLACK to BLANK

1.44

1.44

0

0

1

00H

BLANK LEVEL

7.62

0

0

1

0

xxH

SYNC LEVEL

0

0

0

0

0

xxH

NOTE

Typical with full-scale IOG = 26.67 mA.