SL5067

4

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

mV, see Fig. 3.

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.

f

1

2

p LC

The Q factor of the TANK is given by.

Q

+ 1770

2

pf

+ 1770

2

pf

The Q factor of the coil must be high, e.g. >20

Good temperature stability can be achieved by the correct

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

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”

MODULATED RF OUTPUT

The modulated RF outputs from pin 1 and pin 2 consist of

via 75

W resistors. Great care must be taken with the

decoupling of the supply to these outputs.

Both outputs are suitable for driving either 75

W line, or for

connection to a balun or impedance matching transformer.

This has the added benefit of minimising common mode

coupling, thus giving improved RF performance.

87

85

83

81

79

0.0

1.0

2.0

3.0

4.0

5.0

80dB

mV

1.4

2.45

VOLTAGE SET ON PIN 3

Fig. 4. Picture carrier, unmodulated RF output level

77