THS7376 Datasheet, PDF (45/61 Pages) Texas Instruments – 4-Channel Video Amplifier with One SD and Three HD 8th-Order Filters with 6-dB Gain

THS7376
www.ti.com
SBOS692 – JUNE 2013
For 720p, 1080i, and 1080p signals, or for the 480i, 576i, 480p, and 576p signals with sync present on the P’_B
and P’_R channels, the lowest voltage of the sync is –300 mV below the midpoint reference voltage of 0 V. The
P’_B and P’_R signals allow a signal to be as low as –350 mV below the midpoint reference voltage of 0 V. This
allowance corresponds to 100% yellow for the P’_B signal or 100% cyan for the P’_R signal . Because the P’_B and
P’_R signal voltage can be lower than the sync voltage, there is a potential for clipping the signal over a short
period of time if the signals drop below the sync voltage.
The THS7376 includes a 105-mV input level shift, or 210 mV at the output, that should mitigate any clipping
issues. For example, if an STC is used, then the bottom of the sync is 210 mV at the output. If the signal does go
the lowest level, or 50 mV lower than the sync at the input, then the instantaneous output is [(–50 mV + 105 mV)
× 2 = 110 mV] at the output.
Another potential risk is that if this signal (100% yellow for P’_B or 100% cyan for P’_R) exists for several pixels,
then the STC circuit engages to raise the voltage back to 0 V at the input. This function can cause a 50-mV level
shift at the input midway through the active video signal. This effect is undesirable and can cause errors in the
decoding of the signal. Therefore, TI recommends using ac-bias mode for component P’_B and P’_R signals when
ac-coupling is desired.
Copyright © 2013, Texas Instruments Incorporated
Product Folder Links: THS7376
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