U4935B Datasheet, PDF (10/16 Pages) TEMIC Semiconductors – SECAM Decoder

U4935B
Identification
The identification circuit is a quadrature-type FM
demodulator which uses the bell filter as a phase shifter.
The resonance frequency of the phase shifter is adjusted
* to 4.33 MHz i.e., the frequency between the 4.25-MHz
* (B–Y) carrier and the 4.40625-MHz (R–Y) carrier
during burst gating. The output of the ACC is multiplied
with the output of the phase shifter. The sample-and-hold
circuit samples the output of the multiplier during burst
gating and maintains this value outside of the burst-gate
pulse time. The identification and killer detectors
compare the sampled-and-hold voltage with internal
detection levels. Only line identification (and no field
identification) is implemented.
The identification circuit must communicate with the
U4930B (PAL/NTSC decoder) to guarantee that the out-
put signal from the decoder is available when no PAL
signal has been identified.
If a SECAM signal has been decoded, a request for
“color on” is transmitted to Pin 1 (current sink: 180 mA).
If the signal request is grated (i.e., Pin q is “HIGH”
therefore no PAL), the output signals from the U4935B
are switched on and the output pins of the U4930B have
a high impedance.
If no SECAM signal has been decoded, the outputs of the
U4935B will be blanked or have high-impedance state
depending on the logic level at Pin 1.
(see table 1)
System Identification of
the U4930B
No PAL
PAL
Logic Level; Pin 1 of
the U4935B
HIGH (5.0 V)
LOW (1.5 V)
SECAM Identification of
the U4935B
SECAM; 180 mA
no SECAM; 0 mA
SECAM; 180 mA
no SECAM; 0 mA
Output Pins 9, 10 of
the U4935B
(–R–Y), –(B–Y) signals
Blanked
High impedance
CVBS
in
16
ACC
VBLK
BGP
fH
2
Bell
filter
S/H
Bell-filter
output
Identification
detector
output
9611722
Killer
detector
output
Figure 19. Block diagram of the identification
10 (16)
TELEFUNKEN Semiconductors
Preliminary Information
Rev. A1, 28-Jan-97