Zenith D52WLCD Series, Service Manual

D52WLCD

22

CIRCUITS

CIRCUIT DESCRIPTIONS

1.2 CXA2151Q :

Video/Sync Selector

(1) Description

The CXA2151Q is a bipolar IC developed for multi scan TVs,
and incorporates a four system video switch (including HV
sync signal processing) and a YCbCr output matrix circuit.

(2) Features

• Supports the I

2

C bus

• Supports multi scan
• Four system video switch (of which two systems support D3

pins)

• Matrix circuit
• Each YCbCr output can be switched between 0dB, 6dB

(gain adjustable) and mute.

• Sync signal automatic identification circuit (with fixed mode)
• Sync separation circuit (supports HD)
• HD Tri-level sync identification circuit
• Sync signal frequency counter (both H and V)
• Dummy sync output

(3) Description of Operation

1) Programmable Matrix Selector

The CXA2151Q has a built-in four system video switch,
which can be selected by INPUT_SEL (I

2

C bus).

YCbCr, HD YPbPr, GBR and the respective HV sync sig-
nals can be input to each system.
Horizontal scanning line frequencies from 15 to 45kHz can
be input as the range which supports multi scan.
The selected signals are output from SEL_OUT (Pins 22,
23, 25, 26 and 27), respectively. The output amplitude at
this time can be selected by GAIN_SEL (I

2

Cbus), but

when GAIN_SEL is set to 0, the gain can be adjusted by
YGAIN, CBGAIN and CRGAIN (I

2

C bus).

HV sync signal input supports both positive and negative
polarity.

Select MAT_OUT (I

2

C bus) as follows according to the input.

• Select THROUGH mode during YCbCr input.
• When YPbPr or GBR are input, select the mode that con-

verts these signals to YCbCr.

The matrix conversion formulas are shown below.

[MAT_OUT = 1: Y

HD

PbPr

$

YCbCr]: CCIR protocol

Y = YHD + 0.094Pb + 0.196Pr
Cb = 0.564 (1.762Pb – 0.196Pr)
Cr = 0.713 (–0.094Pb + 1.379Pr)

[MAT_OUT = 2: Y

HD

PbPr

$

YCbCr]: BTA protocol

Y = YHD + 0.068Pb + 0.191Pr
Cb = 0.564 (1.758Pb – 0.191Pr)
Cr = 0.713 (–0.068Pb + 1.385Pr)

[MAT_OUT = 3: GBR 

$

YCbCr]

Y = 0.3R + 0.59G + 0.11B
Cb = 0.564 (–0.3R – 0.59G + 0.89B)
Cr = 0.713 (0.7R – 0.59G – 0.11B)

In addition, the IN1 and IN2 systems support D3 input pins.
This is selected by SELSTB_1 and SELSTB_2 (I

2

C bus).

The control line input voltage of each L1, L2, L3 and SW pin
is returned to the status register by a ternary or binary value.

Next, the HV sync signal processing block is described
below.
Existence distinction is first performed to determine whether
the selected sync signals are input from H and V, and these
results are sent as the existence status to the EV and EH
status registers. On the other hand, polarity-matched H and V
that passed through the polarity identification circuit are input
to the priority ranking circuit.
When inputting composite sync (CS), input to the H input pin
of each input system. After passing through the polarity iden-
tification circuit, V sync separation is performed and the sig-
nal is input to the priority ranking circuit.
When inputting Sync on Y or Sync on Green, input to the
number 3 pin of each input system.
After passing through HYSW, the signal is amplified by 6dB
and output to YG_OUT (Pin 15). This output is returned to
YG_IN (Pin 16) via a sync tip clamping capacitor, sync sepa-
ration is performed, and the signal is input to the priority rank-
ing circuit. This route can also be used during CS signal input
by setting HYSW (I

2

C bus) to 1.

In addition, sync identification is performed to determine
whether the input signal from YG_IN (Pin 16) is Tri-level
sync, and these results are returned to the 3STATE status
register.
In this manner, the respective signals are input to the priority
ranking circuit, and the output sync signal is determined by
the EV and EH status.

The priority ranking is as follows. The TV set should be
designed so that one of the following three points is met.

1. When both H and V exist at the H and V pins, these sig-

nals are selected with the highest priority.

$

EH = 1, EV = 1

2. When CS exists at the H pin and there is no input at the V

pin, CS is selected.

$

EH = 1, EV = 0

3. When Y or GREEN exists at the number 3 pin and there is

no input at the H and V pins, Y or GREEN is selected.

$

EH = 0, EV = 0

After the HV output is determined, the H sync signal pulse
width is adjusted by H_WIDTH (I

2

C bus), and then

the H sync signal is output together with the V sync signal to
SEL_OUT.

2) SYNC Counter

The H and V sync signals selected by the HV sync signal
processing block described previously are sent to the SYNC
counter block next.
The SYNC counter block counts the frequency of the input H
and V sync signals.