Description Of The Block Diagram - Philips PM 5508 Operating Manual

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IV. DESCRIPTION OF THE BLOCK DIAGRAM
(See Fig. IV-1)
To obtain a constant ratio between line synchronising pulses, field synchro-
nising pulses and the various patterns, the circuits of the instrument are
controlled by a master oscillator. The frequency of this oscillator (312.5 kHz)
is divided by means of a 2 : 1 divider in order to obtain the pulses "a", which
control the horizontal information in the patterns. This divider is followed by
another 2 1 divider and a 5
1 divider in order to obtain pulses of line
frequency ("Ib" and "Is").
Furthermore, the line frequency is successively divided by 2, by 4, by 3, and
by 13 in order to obtain pulses shaving the field frequency ("fb" and "fs").
These dividers also supply pulses to control the vertical information in the
patterns ("24 I", "312 I", from which are derived "~ b" and "96 I").
The luminance signal, the black/white patterns, the convergence patterns and
the composite sychronising and blanking signal are generated on the basis
of the afore mentioned horizontal and vertical control pulses.
These signals are added in the luminance-sync.-blanking adder and passed
on, via the delay Fine, the video amplifier, where the composite luminance
signal is added to the chrominance signal. The delay line (0.375 ,us) com-
pensates for the •time delay which arises when the colour signals are encoded.
The R, G, and B signals are generated in the colourbar generator. This gene-
rator is followed by a matrix, "adding" the R, G, and B signals in such a way
that the correct Y, (R-Y), and (B-Y) signals are obtained. The step signal
(Y') of the greyscale signal is also generated in this matrix.
The colour subcarrier signal is supplied by acrystal-controlled oscillator. The
phase of the subcarrier to the (B-Y) modulator is shifted 90° in a phase
shifting circuit, in order to obtain the correct quadrature of (R-Y) and (B-Y).
In a PAL switching circuit the phase of the subcarrier to the (R-Y) modulator
is inverted line sequentially, in order to obtain the PAL encoding. The PAL
switching circuit can be cut out during the moments, that the generator has
to produce an NTSC encoded signal (test signal "DELAY"). During this
signal, however, the PAL switch actually operates briefly during the line
backporch to produce the PAL-alternating burst. This is controlled by the " 2 I' "
pulses. The colour-deference signals and the burst keying pulses {the latter
are derived from the "Is" pulses) are applied to the (R-Y) and (B-Y) modula-
tors. These modulators are balanced modulators together supplying the chromi-
nance signal in which the carrier wave has been suppressed. The chrominance
signal is added to the luminance signal in the video amplifier.
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