Hitachi CG2026S, Service Manual

Page: 5 / 42

4
2.6 Chroma and luminance processing:
The chroma decoder is able to demodulate PAL, NTSC and SECAM signals. The decoder dedicated to PAL and NTSC
sub-carrier is based on a synchronous demodulator, and an Xtal PLL locked on the phase reference signal (burst).
The SECAM demodulation is based on a PLL with automatic calibration loop.
The color standard identification is based on the burst recognition.
Automatic and forced modes can be selected through the I2C bus.
NTSC tint, and auto flesh are controlled through I2C bus.
Xtal PLL can handle up to 3 crystals to work in PAL M, PAL N and NTSC M for South America.
ACC an ACC overload control the chroma sub-carrier amplitude within 26dB range. Both
ACC s are based on digital systems and do not need external capacitor.
All chroma filters are fully integrated and tuned via a PLL locked on Xtal VCO signal.
A second PLL is used for accurate fine-tuning of the SECAM bell filter. This tuning is achieved during the frame blanking.
An external capacitor memorizes the bell filter tuning voltage.
A base-band chroma delay-line rebuilds the missing color line in SECAM and removes transmission phase errors in PAL.
The base-band chroma delay line is clocked with 6MHz signal provided by the horizontal scanning VCO.
The luminance processor is composed of a chroma trap filter, a luminance delay line, a peaking function with noise coring
feature, a black stretch circuit.
Trap filter and luminance delay lines are achieved with the use of bi-quad integrated filters, auto-aligned via a master filter
phase locked loop.
2.7 RGB output circuit:
The video processor performs the R, G, B processing.
There are three sources:
1 . Y,U,V inputs (coming from luma part (Y output), and chroma decoder outputs (R-Y, B-Y outputs).
2 . External R,G,B inputs from SCART (converted internally in Y,U,V), with also the possibility to input YUV signals from
a DVD player, (YUV specification is Y=0.7 V PP , U= 0.7 V PP , V = 0.7V PP for 100% color bar).
3 . Internal R,G,B inputs (for OSD and Teletext display)
The main functions of the video part are:
n Y,U,V inputs with integrated clamp loop, allowing a DC link with YUV outputs,
n External RGB inputs (RGB to YUV conversion), or direct YUV inputs,
n Y,U,V switches,
n Contrast, saturation, brightness controls,
n YUV to RGB matrix,
n OSD RGB input stages (with contrast control),
n RGB switches,
n APR function,
n DC adjustment of red and green channels,
n Drive adjustments (R, G, B gain),
n Digital automatic cut-off loop control,
n Manual cut-off capability with I2C adjustments,
n Half tone, oversize blanking, external insertion detection, blue screen,
n Blanking control and RGB output stages.
2.8 µ-Controller
The ST92195 is the micro-controller, which is required for a color TV receiver. ST92195D1 is the version with one page
Teletext and ST92195D7 is the one with 7 page Teletext. The IC has the supply voltages of 5 V and they are mounted in
PSDIP package with 56 pins.
µ-Controller has the following features
n Display of the program number, channel number, TV Standard, analogue values, sleep timer, parental control and
mute is done by OSD
n Single LED for standby and on mode indication
n System configuration with service mode
n 3 level logic output for SECAM and Tuner band switching