MC1374P Motorola, MC1374P Datasheet - Page 3

• Manufacturer Part Number: MC1374P
• Description: TV MODULATOR CIRCUIT
• Manufacturer: Motorola

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
V CC.
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
R10
MOTOROLA ANALOG IC DEVICE DATA
The MC1374 contains an RF oscillator, RF modulator, and
The FM system was designed specifically for the TV
Q23
Section
Bias
D1
Q24
R11
Q25
R12
6.0k
5
Gnd
14
Audio In
R14
R15
R13
FM Oscillator/Modulator
325
Q3
R1
Q1
Sound Carrier
Q4
OSC B+
4
R2
Q2
C1
R16
Q26
GENERAL INFORMATION
R17
Figure 2. TV Modulator
Q5
R3
MC1374
Q6
3
Sound Carrier
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).
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 RF modulator and is then modulated onto the AM carrier.
Oscillator
R4
In the circuit above, devices Q1 through Q7 are active in
The modulated FM signal from Pin 3 is coupled to Pin 1 of
Q7
Sound Carrier
Q27
2
1
In
Q12 Q13
R5
Q10
Q8
8
13
V CC
AM Modulator
Gain
12
Q14 Q15
R6
Q9
Q11
RF Out
9
Video In
11
R7
Q21
Q16
AM Oscillator
7
Q19 Q20
RF Tank
R8
6
Q17
R9
Q18
Q22
3