Datasheet

1023
940
817.3 mV
751.1 mV
51.1 mV
255 767511
64
0
Input Digital Codes
Analog Output From DACs
Ramping Analog Output With Clipping Effect on Top and Bottom
Output After
Clipping
Output Before
Clipping
THS8200
www.ti.com SLES032D –JUNE 2002–REVISED JUNE 2013
4.5 Clip/Shift/Multiplier (CSM)
There are limits on the code range of the video data if sampled according to ITU or SMPTE standards. In
other words, the full 10-bit range [0:1023] is not used to represent video pixels. For example, typically 64
decimal is the lowest code allowed to represent a video signal and corresponds to the blanking level.
Similarly for Y, typically the maximum code is 940 decimal. Excursions outside this range can be the result
of digital video processing.
THS8200 can handle such instantaneous excursions in either of two ways: by limiting the input codes to
programmable max/min values, or by allowing such excursions to occur.
Depending on which approach is chosen, the user can scale up the video data in the CSM to make sure
the full-scale dynamic range of the DAC is used for optimal performance when using limiting. Alternatively,
the instantaneous excursions outside the code range can be output by the DAC in the analog output
signal (allowing super-white/black in analog output) when this clipping is disabled.
The CSM block allows the user to specify the behavior of THS8200 with such reduced-swing input video
codes. It consists of the following:
1. An optional clipping of the input video data at a high and low limit, where the limits are individually
programmable per channel.
2. A downward shift of the input video data, where the shift amount is individually programmable per
channel.
3. A multiply (magnitude scaling) function of the video data, where the multiplier coefficient is individually
programmable per channel.
4.5.1 Clipping
Clipping (limiting) of the video input data can be turned on or off on a per-channel basis, and selectively at
the high and/or low end, by programming the csm_<gy,rcr,bcb>_<high,low>_clip_on registers. The
high/low clipping values can be programmed on a per-channel basis using registers
csm_clip_<gy,rcr,bcb>_<high,low>.
Figure 4-5 shows a typical situation to clip ITU-R.BT601 sampled video signals.
Figure 4-5. Effect of Clipping on Analog Output
Copyright © 2002–2013, Texas Instruments Incorporated Detailed Functional Description 25
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