ADV7123 datasheet(13/20 Pages) AD

13 / 20 page

ADV7123

–13–

REV. B

CIRCUIT DESCRIPTION AND OPERATION

The ADV7123 contains three 10-bit D/A converters, with three

input channels, each containing a 10-bit register. Also integrated

on board the part is a reference amplifier. CRT control functions

BLANK and SYNC are integrated on board the ADV7123.

Digital Inputs

Thirty bits of pixel data (color information) R0–R9, G0–G9,

and B0–B9 are latched into the device on the rising edge of each

clock cycle. This data is presented to the three 10-bit DACs and

then converted to three analog (RGB) output waveforms. See

Figure 2.

CLOCK

DATA

ANALOG OUTPUTS

(IOR, IOG, IOB

IOR, IOG, IOB)

DIGITAL INPUTS

(R9–R0, G9–G0, B9–B0,

SYNC, BLANK)

Figure 2. Video Data Input/Output

The ADV7123 has two additional control signals that are

latched to the analog video outputs in a similar fashion.

BLANK

and

SYNC are each latched on the rising edge of CLOCK to

maintain synchronization with the pixel data stream.

The

BLANK and SYNC functions allow for the encoding of

these video synchronization signals onto the RGB video output.

This is done by adding appropriately weighted current sources

to the analog outputs, as determined by the logic levels on the

BLANK and SYNC digital inputs. Figure 3 shows the analog

output, RGB video waveform of the ADV7123. The influence of

SYNC and BLANK on the analog video waveform is illustrated.

Table I details the resultant effect on the analog outputs of

BLANK and SYNC.

All these digital inputs are specified to accept TTL logic levels.

Clock Input

The CLOCK input of the ADV7123 is typically the pixel clock

rate of the system. It is also known as the dot rate. The dot rate,

and thus the required CLOCK frequency, will be determined by

the on-screen resolution according to the following equation:

Dot Rate = (Horiz Res)

× (Vert Res) × (Refresh Rate)/

(Retrace Factor)

Horiz Res

=Number of Pixels/Line.

Vert Res

=Number of Lines/Frame.

Refresh Rate

=Horizontal Scan Rate. This is the rate at

which the screen must be refreshed,

typically 60 Hz for a noninterlaced system

or 30 Hz for an interlaced system.

Retrace Factor

=Total Blank Time Factor. This takes into

account that the display is blanked for a

certain fraction of the total duration of

each frame (e.g., 0.8).

Table I. Video Output Truth Table (RSET = 530

, RLOAD = 37.5

)

DAC

Description

IOG (mA)

IOR/IOB

SYNC

BLANK

Input Data

WHITE LEVEL

26.67

18.62

3FFH

VIDEO

Video + 8.05

18.62 – Video

Video

18.62 – Video

Data

VIDEO to

BLANK

Video

18.62 – Video

Video

18.62 – Video

Data

BLACK LEVEL

8.05

18.62

000H

BLACK to

BLANK

18.62

000H

BLANK LEVEL

8.05

18.62

xxxH

SYNC LEVEL

18.62

xxxH

RED, BLUE

GREEN

18.62

0.7

26.67

1.000

8.05

0.3

WHITE LEVEL

BLANK LEVEL

SYNC LEVEL

100 IRE

43 IRE

NOTES:

1. OUTPUTS CONNECTED TO A DOUBLY TERMINATED 75

LOAD.

2. VREF = 1.235V, RSET = 530 .

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

Figure 3. RGB Video Output Waveform

ADV7123 Datasheet(PDF) 13 Page - Analog Devices

ADV7123 Datasheet(HTML) 13 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Datasheet Download

Link URL