Input Selector; Signal Levels And Gain Control; Synchronization; Chroma Decoder - Daewoo DTF-2950-100D Service Manual

CP-850FX Service Manual
and SECAM operation a baseband delay line is used for U and V signals. This can be used as
comb filter in NTSC operation (only for chrominance). The RGB input from SCART is used as an
overlay for the CVBS channel (RGB+FBL).
This block contains a matrix (for RGB signals).

5.4.1.2 Input Selector

The analog CVBS or SVHS luma signal are fed to the inputs CVBS1...7 of VSP94x2A
(amplitude 0.5...1.5 V pp ). One signal is selected and fed to the first ADC. A second signal
(SVHS Chroma) can be selected and fed to the other ADC. After clamping to the back porch
both signals are AD-converted with an amplitude resolution of 9 bit. The AD conversion is done
using a 20.25 MHz free-running stable crystal clock. Before the A to D conversion the signals are
lowpass filtered to avoid antialias effects. One input is looped back to output CVBSO1(#63). A
signal addition is performed to output a CVBS signal even when separate Y/C signals are used
at input.

5.4.1.3 Signal Levels And Gain Control

To adjust to different CVBS input voltages a digitally working automatic gain control is
implemented. Input voltages in the range between 0.6 to 1.8 V pp can be applied to the CVBS
inputs.

5.4.1.4 Synchronization

After elimination of the high frequent components of the CVBS signal by a low pass filter,
horizontal and vertical sync pulses are separated. Horizontal sync pulses are generated by a
digital phase locked loop. The time constant is adjusted between fast and slow behaviour to
accommodate different input sources (e.g. VCR).

5.4.1.5 Chroma Decoder

The digital multistandard chroma decoder is able to decode NTSC and PAL signals with a
subcarrier frequency of 3.58 MHz and 4.43 MHz as well as SECAM signals with automatic
standard detection. The TV controller software has configured the colour decoder to operate in
automatic detection mode. When the signal source comes from the tuner, only SECAM and PAL
(50Hz) standard are enabled. In AV mode or when program number 0 is selected the following
standards are also enabled : NTSC M, NTSC 4.43 and PAL 60.
The demodulation is done with a regenerated colour-carrier.

5.4.1.6 Luminance Processing

A luminance notch filter is implemented to separate the chroma information from the luminance.
Depending on the colour standard, one out of three different notch characteristics is chosen
('PAL', 'NTSC', 'SECAM') automatically.

5.4.1.7 RGB Front-End

An analogue RGB input port for an external RGB source is available. The incoming signal is
clamped to the back porch by a clamping pulse. This input as an overlay input (soft mix). The
RGB signal must then be synchronised to the main CVBS/YC signal.

5.4.1.8 Signal Processing

5.3.1.8.1 Horizontal Prescaler

The main application of the horizontal prescaler is the conversion of the number of pixels coming
form the 40.5/20.25 MHz pixel clock domain down to the number of pixels stored in the memory
(factor 2/3). Generally the number of incoming pixels can be decimated by a factor between 1
and 64 in a granularity of 2 output pixels. The horizontal scaler reduces the number of incoming
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