THS8135 Datasheet, PDF (11/23 Pages) Texas Instruments – TRIPLE 10-BIT, 240 MSPS VIDEO DAC WITH TRI-LEVEL SYNC AND VIDEO (ITU-R.BT601) COMPLIANT FULL SCALE RANGE

THS8135
TRIPLE 10-BIT, 240 MSPS VIDEO DAC WITH TRI-LEVEL SYNC AND VIDEO
(ITU-R.BT601)—COMPLIANT FULL SCALE RANGE
SLAS343A – MAY 2001 – REVISED JUNE 2002
Illegal Color
Difference Outputs
Input ^VO
Codes mV
1023 800
960 700
300 mV
800 mV
700 mV
512 400
300 mV
64 50
0
0
0
Figure 4. CbCr Outputs, Reduced-Scale Input Code Range
output amplitude control
The current drive on all three output channels (including sync) is controlled by a resistor R_FS that must be
connected between FSADJ and AVSS. In all operation modes the relative amplitudes of these current drivers
are maintained irrespective of the R_FS value, as long as a maximum current drive capability is not exceeded.
Therefore, a 7:3 video to sync ratio is preserved when adjusting R_FS.
The sync generator is composed of different current sources that are internally routed to a corresponding DAC
output. Since they are additional to the video DACs, full 10-bit DAC resolution is preserved for video. Depending
on the setting of INS3_INT during SYNC low, the sync current drive is added to either only the green channel
output (sync-on-G/Y) if INS3_INT=L or all three channel outputs (sync-on-all) if INS3_INT=H. Sync insertion
is only available in video DAC mode.
Figure 5 shows the relationship between R_FS and the current drive level on each channel for full-range DAC
input. When using reduced-scale range, the codes on the G/Y channel are not internally scaled (only BCb and
RCr channels are scaled). Therefore, the user should increase the DAC full-scale current by decreasing R_FS
by a factor of 1023/(940-64) to map the reduced-scale Y input code range to the same output current drive level.
Since these are the current drive levels for the video DACs they do not take into account the additional dc bias
for sync insertion when using video DAC mode. The voltage compliance outputs in Figure 5 assume termination
with a 37.5-Ω resistor.
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