MC1374 View Datasheet(PDF) - Motorola => Freescale
Part Name
Description
Manufacturer
MC1374 Datasheet PDF : 10 Pages
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Bias
Section
MC1374
Figure 2. TV Modulator
FM Oscillator/Modulator
Sound Carrier
Audio In
OSC B+
14
4
Sound Carrier
Oscillator
3
2
AM Modulator
VCC
RF Out
8
9
AM Oscillator
RF Tank
76
R10
R11
R12
6.0k
R16
Q1 Q2
R13
325
Q25
Q24
R14
Q3
R15
Q23
R17
C1
Q6
Q4
Q5
Q26
Q7
Q21
Q22
Q12 Q13
Q14 Q15
Q19 Q20
Q10
Q11
Q27
Q8
Q9
Q16
Q17
Q18
D1
R1
R2
R3
5
Gnd
R4
R5
R6
R7
R8
R9
1
Sound Carrier
In
13 12
Gain
11
Video In
GENERAL INFORMATION
The MC1374 contains an RF oscillator, RF modulator, and
a phase shift type FM modulator, arranged to permit good
printed circuit layout of a complete TV modulation system.
The RF oscillator is similar to the one used in MC1373, and is
coupled internally in the same way. Its frequency is controlled
by an external tank on Pins 6 and 7, or by a crystal circuit, and
will operate to approximately 105 MHz. The video modulator
is a balanced type as used in the well known MC1496.
Modulated sound carrier and composite video information
can be put in separately on Pins 1 and 11 to minimize
unwanted crosstalk. A single resistor on Pins 12 and 13 is
selected to set the modulator gain. The RF output at Pin 9 is
a current source which drives a load connected from Pin 9 to
VCC.
The FM system was designed specifically for the TV
intercarrier function. For circuit economy, one phase shift
circuit was built into the ship. Still, it will operate from 1.4 MHz
to 14 MHz, low enough to be used in a cordless telephone
base station (1.76 MHz), and high enough to be used as an
FM IF test signal source (10.7 MHz). At 4.5 MHz, a deviation
of ± 25 kHz can be achieved with 0.6% distortion (typical).
In the circuit above, devices Q1 through Q7 are active in
the oscillator function. Differential amplifier Q3, Q4, Q5, and
Q6 acts as a gain stage, sinking current from input section
Q1, Q2 and the phase shift network R17, C1. Input amplifier
Q1, Q2 can vary the amount of “in phase” Q4 current to be
combined with phase shifter current in load resistor R16. The
R16 voltage is applied to emitter follower Q7 which drives an
external L–C circuit. Feedback from the center of the L–C
circuit back to the base of Q6 closes the loop. As audio input
is applied which would offset the stable oscillatory phase, the
frequency changes to counteract. The input to Pin 14 can
include a dc feedback current for AFC over a limited range.
The modulated FM signal from Pin 3 is coupled to Pin 1 of
the RF modulator and is then modulated onto the AM carrier.
MOTOROLA ANALOG IC DEVICE DATA
3
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