TDA8505 Datasheet, PDF (6/32 Pages) NXP Semiconductors – SECAM encoder

Philips Semiconductors
SECAM encoder
Preliminary specification
TDA8505
FUNCTIONAL DESCRIPTION
The following three important circuits are integrated:
• Encoder circuit
• Modulator control circuit
• Sync separator and pulse shaper.
Encoder circuit
INPUT STAGE
R, G and B inputs are connected to the matrix via a
clamping and a blanking circuit.
For an EBU colour bar of 75% the amplitude of the signal
must be 0.7 V (peak-to-peak value). The outputs of the
matrix are Y, D'R and D'B.
The second part of the input stage contains inputs for
colour difference signals and a luminance signal. The
condition for 75% colour bar is
−(R−Y) = 1.05 V (peak-to-peak value) at pin 1,
−(B−Y) = 1.33 V (peak-to-peak value) at pin 3 and
Y = 1 V (peak-to-peak value) without sync at pin 5. After
clamping and blanking the amplitude and polarity are
corrected such that the signals are equal to the signals of
the matrix output. Signals are connected to a switch. Fast
switching between the two input parts is possible by the
multiplexer control pin (pin 2).
The Y output signal of the multiplexer is added to the sync
pulse of the sync separator.
The Y input (pin 5) is different to the other 5 inputs. The
timing of the internal clamping is after the sync period and
there is no vertical blanking.
The input blanking of Y can be switched off by a HIGH at
pin 12, and the internal sync separator signal is not added
to the Y signal. In this way the Y+SYNC is allowed at pin 5
and after clamping internally connected directly to pin 25.
The colour difference signals are switched sequentially by
H/2 and fed to the low frequency pre-emphasis circuit.
The colour-killing input signal at pin 28 can be used for
completely blanking the internal colour difference signals
at the input of the low frequency pre-emphasis filter.
LOW FREQUENCY PRE-EMPHASIS
This filter is fully integrated, Fig.3 illustrates the nominal
response.
The transfer is guaranteed within the illustrated area for
the whole ambient temperature range by a compensation
circuit.
4
handbook, full pagewidth
H
(dB)
2
0
2
4
6
8
10
10 ⁴
July 1994
MLA953 - 1
10 ⁵
10 ⁶
f (Hz)
10 ⁷
Fig.3 Nominal response for the low frequency pre-emphasis filter.
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