G2R-14-12VDC Datasheet, PDF (12/73 Pages) Texas Instruments – Ultralow Power NTSC/PAL/SECAM Video Decoder With RObust Sync Detector

2 Functional Description
2.1 Analog Front End
The TVP5150A decoder has an analog input channel that accepts two video inputs, which are ac-coupled. The
decoder supports a maximum input voltage range of 0.75 V; therefore, an attenuation of one-half is needed for most
input signals with a peak-to-peak variation of 1.5 V. The maximum parallel termination before the input to the device
is 75 Ω. The two analog input ports can be connected as follows:
• Two selectable composite video inputs or
• One S-video input
An internal clamping circuit restores the ac-coupled video signal to a fixed dc level.
The programmable gain amplifier (PGA) and the AGC circuit work together to make sure that the input signal is
amplified sufficiently to ensure the proper input range for the ADC.
The ADC has 9 bits of resolution and runs at a maximum speed of 27 MHz. The clock input for the ADC comes from
the PLL.
2.2 Composite Processing Block Diagram
The composite processing block processes NTSC/PAL/SECAM signals into the YCbCr color space. Figure 2−1
explains the basic architecture of this processing block.
Figure 2−1 illustrates the luminance/chrominance (Y/C) separation process in the TVP5150A decoder. The
composite video is multiplied by subcarrier signals in the quadrature modulator to generate the color difference
signals Cb and Cr. Cb and Cr are then low-pass (LP) filtered to achieve the desired bandwidth and to reduce crosstalk.
An adaptive 4-line comb filter separates CbCr from Y. Chroma is remodulated through another quadrature modulator
and subtracted from the line-delayed composite video to generate luma. Contrast, brightness, hue, saturation, and
sharpness (using the peaking filter) are programmable via I²C.
The Y/C separation is bypassed for S-video input. For S-video, the remodulation path is disabled.
2.3 Adaptive Comb Filtering
The 4-line comb filter can be selectively bypassed in the luma or chroma path. If the comb filter is bypassed in the
luma path, then chroma notch filters are used. TI’s patented adaptive 4-line comb filter algorithm reduces artifacts
such as hanging dots at color boundaries and detects and properly handles false colors in high frequency luminance
images such as a multiburst pattern or circle pattern.
2.4 Color Low-Pass Filter
In some applications, it is desirable to limit the Cb/Cr bandwidth to avoid crosstalk. This is especially true in case of
video signals that have asymmetrical Cb/Cr sidebands. The color LP filters provided limit the bandwidth of the Cb/Cr
signals.
Color LP filters are needed when the comb filtering turns off, due to extreme color transitions in the input image.
Please refer to Section 2.20.26, Chrominance Control #2 Register, for the response of these filters. The filters have
three options that allow three different frequency responses based on the color frequency characteristics of the input
video.
2−1