ADV7129 datasheet(13/20 Pages) AD

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ADV7129

–13–

REV. 0

DIGITAL-TO-ANALOG CONVERTERS (DACS)

AND VIDEO OUTPUTS

The ADV7129 contains three high speed video DACs. The

DAC outputs are represented as the three primary analog color

signals IOR (red video), IOG (green video) and IOB (blue

video).

DACs and Analog Outputs

The part contains three matched 8-bit digital-to-analog converters.

The DACs are designed using an advanced, high speed, seg-

mented architecture. The bit currents corresponding to each

digital input are routed to either IOR, IOG, IOB (bit = “1”) or

IOR

, IOG, IOB (bit = “0”). Normally IOR, IOG, & IOB are

connected to GND.

ZO = 50Ω

(CABLE)

ZL = 50Ω

(MONITOR)

IOR, IOG, IOB

DACs

ZS = 50Ω

(SOURCE TERMINATION)

Figure 10. DAC Output Termination (Doubly Terminated

Ω Load)

The analog video outputs are high impedance current sources.

Each of the these three RGB current outputs are specified to di-

rectly drive a 25

Ω load (doubly-terminated 50 Ω).

Reference Input and RSET

An external 1.235 V voltage reference is preferred to set up the

analog outputs of the ADV7129. The reference voltage is con-

nected to the VREF input. In the absence of an external refer-

ence, the on-chip voltage reference is internally connected to

the VREF pin. The internal reference will set up the DAC cur-

rents, although with slightly less accuracy.

A resistor RSET is connected between the RSET (RRSET, RGSET,

RBSET) input of the part and ground. An RSET value of 280

Ω

corresponds to the generation of two times RS-343A video lev-

els into a doubly-terminated 50

Ω load. Figure 11 illustrates the

resulting video waveform and the Video Output Truth Table il-

lustrates the corresponding control input stimuli. On the

ADV7129 SYNC can be encoded on any of the analog signals,

however in practice, SYNC is generally encoded on either the

IOG output or on all of the video outputs.

Any combination of RSET, DAC termination resistors and

programming of SYNC and pedestal are possible provided that

the maximum DAC current of 60 mA and the DAC output

compliance specifications are adhered to. The following tables

show the current levels for different values of RSET resistors and

RLOAD termination.

7.5 IRE

92.5 IRE

40 IRE

SYNC LEVEL

BLANK LEVEL

BLACK LEVEL

WHITE LEVEL

Figure 11. Composite Video Waveform SYNC Decoded;

Pedestal = 7.5 IRE

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