Blanking Generation

Sync Generation

Device Configuration

DAC Operation

THS8136

The BLANK control input forces the output amplitude on all channels to the blanking or reference level,

irrespective of the value on the data input ports. The output blanking level on each channel and its relation to

active video varies depending on the mode of operation. In generic DAC mode, the output blank level for each

selected for 700-mV output) is applied to provide room for bi-level sync insertion. When RGB sync insertion is

enabled, the output blank level of each DAC will be at 350 mV and will correspond to a DAC input code of 0. In

YPbPr video mode, the blank level of each DAC is 350 mV, but the AR and AB blank levels correspond to a DAC

input code of 512 to accommodate mid-level UV blank levels. A video to blank level amplitude ratio of 2:1 is

The SYNC and SYNC_T control inputs can be used to enable the superposition of a bi-level sync on the AG

DAC output. Correctly timed assertion of the SYNC input (active low) allows insertion of an analog composite

sync on the AG DAC output consisting of horizontal sync and vertical sync. The video to sync amplitude ratio is

7:3 providing a 300 mV sync tip, when FSADJ is selected to provide 700 mV full-scale graphics or video. This

insertion.

The THS8136 operating mode is determined from the state of the SYNC, SYNC-T, M1, and M2 control terminals.

YPbPr video mode can be selected for support of mid-level PbPr blanking by connecting the sync control input to

modes. See Table 1 and Figure 4, Figure 5, and Figure 6 for additional information on configuring the THS8136.

Table 1. Table 1. Device Configuration

OPERATING MODE

M1

M2

SYNC_T

SYNC

DESCRIPTION

Sync insertion disabled. The blank level on all DAC outputs corresponds

Generic DAC

0

0

1

1

to 0-V and DAC input code 0.

DC bias and sync insertion enabled. The blank level on all DAC outputs

RGB Sync Insertion

0

0

0

SYNC

corresponds to DAC input code 0.

DC bias and sync insertion enabled. AB and AR mid-level blanking

YPbPr Sync Insertion

0

SYNC

0

SYNC

corresponds to DAC input code 512.

The DAC output drivers generate a current with a drive level that can be user-modified by choosing an

such that the relative amplitudes of sync, blank, and graphics/video are always equal to their nominal

and the current drive level on each channel for full-range DAC input. The voltage compliance outputs in Figure 3

assume termination with a 37.5-

Ω resistor. When sync insertion is enabled, an additional current source is

suitable for most applications requiring 700-mV output levels.

Copyright © 2008, Texas Instruments Incorporated

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