SL5067
VIDEO
The video signal is applied to pin 4 via a coupling capacitor,
(see Fig.9). This capacitor provides both clamping and black
level hold. The internal peak white AGC can cope with an input
signal of between 0.5 and 1.5 volts peak to peak.The full 9.5
dB AGC range is handled within a 600mV span on this storage
capacitor.
Pin 3 (MOD INDEX) is used to control both RF carrier
amplitude and video polarity, see Fig. 3. Since the video input
is internally AGC’d, varying the carrier amplitude will also
adjust the video modulation index, see Fig. 4.
For example, for a negative modulation (PAL or NTSC) with
an 80% modulation index, pin 3 should be set to 1.1Volts (see
Fig. 4). This voltage corresponds to an unmodulated RF
output level of 82dB V, see Fig. 3.
The Q factor of the coil must be high, e.g. >20
Good temperature stability can be achieved by the correct
choice of temperature coefficients for C
sound
and L
sound
.
The Audio signal should be coupled into pin 17 via a 470nF
capacitor. The maximum input level is 1 volts peak to peak.
Selection of AM or FM sound is made via pin 18
(FMAMSEL). The DC value on this pin controls the level of the
sound subcarrier. The crossover point between FM and AM
sound occurs at V
CC
(measured at pin 18). Below this
voltage, the modulator is set to FM sound; above it to AM.
Graphs for AM and FM sound subcarrier output levels are
shown in Figs. 6 and 7.
If AM sound is required, it is recommended that a
modulated carrier is fed into the Audio input. Further details of
this are mentioned at the end of the datasheet in the paragraph
marked ‘‘Positive Modulation”
�½
m
AUDIO
The sound IF oscillator can operate from 4.5MHz to
6.5MHz to cover all sound standards. The centre frequency is
determined by the Sound IF Tank LC connected between pins
15 and 16.
The centre frequency is given by.
MODULATED RF OUTPUT
The modulated RF outputs from pin 1 and pin 2 consist of
open collectors which should be externally connected to V
CC
via 75 resistors. Great care must be taken with the
decoupling of the supply to these outputs.
Both outputs are suitable for driving either 75 line, or for
connection to a balun or impedance matching transformer.
W
f
0
+
2
p
1LC
1770
+
2
p
f L
+
1770
0
W
The Q factor of the TANK is given by.
Q
2 f
0
C
p
This has the added benefit of minimising common mode
coupling, thus giving improved RF performance.
87
85
83
81
79
77
0.0
1.0 1.4
2.0 2.45
3.0
VOLTAGE SET ON PIN 3
4.0
5.0
80dB V
m
Fig. 4. Picture carrier, unmodulated RF output level
GEC [ GENERAL ELECTRIC COMPANY ]
