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MC1372 Schematic ( PDF Datasheet ) - Motorola Semiconductors

Teilenummer MC1372
Beschreibung Color TV Video Modulator
Hersteller Motorola Semiconductors
Logo Motorola Semiconductors Logo 




Gesamt 8 Seiten
MC1372 Datasheet, Funktion
® MOTOROLA
MC1372
COLOR TV VIDEO MODULATOR
... an mtegrated circuit used to generate an RF TV signal from
baseband color-difference and luminance signals.
The MC1372 contains a chroma subcamer oscillator, a lead and
lag network, a quasi-quadrature suppressed carrier DSB chroma
modulator, an RF oscillator and modulator, and an LSTTL com-
patrble clock driver with adjustable duty cycle.
The MC1372 is a companion part to the MC6847 Video Display
Generator, providmg and accepting the correct de interconnection
levels. This device may also be used as a general-purpose modulator
wtth a variety of vtdeo signal generating devices such as video games,
test equipment, video tape recorders, etc.
• Single 5.0 Vdc Supply Operation for NMOS
and TTL Compatibility
• Minimal External Components
• Compatible with MC6847 Video Display Generator
• Sound Carrier Addition Capability
• Modulates Channel 3 or 4 Carrier with Encoded Vrdeo Signal
• Low Power Dissipation
• Linear Chroma Modulators for High Versatrlity
• Composrte Vrdeo Signal Generation Capability
• Ground-Referenced Video Prevents Overmodulation
COLOR TV
VIDEO
MODULATOR CIRCUIT
SILICON MONOLITHIC
INTEGRATED CIRCUIT
.~'~~ ~ ~ ~ P SUFFIX
PLASTIC PACKAGE
CASE 646-05
Pin Connections
Duty
Chromtnance
input
Lum1nance
Input
ChrorT;a
1'0odu!ator
Output
FIGURE 1- BLOCK DIAGRAM
Color 8
Input
Lum1flance
1npi..-t
RF
Modulator
Output
Oscillator
Input
Clock
Output
4
Grouna
Duty Cycle
Adjust
Chrorninance
1nput
e----, 41r--+-----t-D Modulator
Outpu"t
Color A
Input
Color
Reference
Input
RF Tank
3-3
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MC1372 Datasheet, Funktion
MC1372
to the phase delayed oscillator signal at the emitter of
associated equ1pment. The duty cycle may be adjusted
buffer transistor 021. The differential signal currents
by varying the de voltage appl1ed to p.n 3. This adjust·
provided by 032 and 033 are switched in trans1stors
ment may be made wtth the use of a potentiOmeter
022 through 025 and the resultant signal voltage is
( 10 kf2} between supply and ground. With no connect•on
developed across R49. This signal has the phase and
to pin 3, the duty cycle is approximately 50"'0.
frequency of the oscillator signal at the emitter of 021.
Chroma Modulator
The amplitude is proportional to the differential input
The chrom1nance oscillator 1s Internally phase sh1fted
signal applied between pins 5 and 6. Transistors 026
and applied to chroma modulators A and B- No external
through 029 and 038-039 form chroma modulator B.
lead/lag networks are necessary. The phase relat1onsh1p
This modulator develops a signal voltage which is propor·
between the modulators IS approx;mately 100°. wh',cb
tiona! to the differential voltage applied between pins
was chosen to orov1de the best rendttJOn of colors us•ng
7 and 6. The phase and frequency of the output is equal
equal amplitude color-difference stgnals. The voltage
to the phase advanced chroma oscillator at the emitter
applied to pin 5, 6. or 7 must always be w1thon the Input
of buffer transistor 020. Both chroma modulators A and
Common Mode Voltage Range S1ncc the amplitude ol
B share the same output resistor, R49, so the output
I signal presented at the em1tter of 042 (pin 8) IS the
algebraic sum of modulators A and B.
The R F oscillator consists of d1fferent1al ampl!f,er
chrominance output is proport10nai to the vo!tage d1f
terence between pms 5 and 6 or 7 and 6, 1t 1S Oes:t able
to select the Color Reference Voltage appl1ed to pm 6 to
be midway between V5max and V5mm (wh1ch shou:d
018 and 019 cross-coupled through em1tter followers
be V7max and V7min1. The Chroma B Modulator w1'l !>e
016 and 017. The oscillator will operate at the parallel
defmed as a (B·YI modulato1 1f a burst ;fag Signal 1S
resonant frequency of the network connected between
applied to the Color B Input (pm 5! at the approp,,ate
pins 13 and 14. The oscillator output is used to sw1tch
time, This voltage should be negat1ve With 1espect to the
the doubly balanced R F modulator, 09 through 015
Color Reference Voltage, and typ1cal~y has an amplttude
Transistors 07 and 08 provide level shifting and a high
equal to 1/2fV6-V5mml. S1nce the phase of bu1st ·S
input impedance to the iummance input pin 9. The
always defmed as -(B Yl. the Ch1 oma A Modulato·
bases of transistors 09 and 010 are both biased through
approx1mates an (R-Yi modu:ato1. hoYI.•ever, the phase
resistors R 17 and R 18, respectively, to the same de
:s offset by 10° ~rom the nommal 90°, to f.JIOV·rle the
reference voltage at 06 emitter. The base voltage at 010
100° phase sh1ft as discussed prev1ously.
may oniy be offset in a negative direction by luminance
signal current source 08. This des1gn msures that over·
RF Modulator and Oscillator
modulation due to the luminance signal will never occur.
The coil and capac1tor connected between p1ns 13 a'1d
The chrominance signal developed at pin 8 is externally
14 should be selected to have a parallel resonance at the
ac coupled to pin 10 where it is reduced by rem tor
carr1er frequency of the des1red TV channel. The values
dividers R 20 and R 17, and added to the fum mance
of 56 pF and 0.1 ,uH shown .n F 1gure 5 we1 e chosen
signal in 09. The resultant differential compos;te v1deo
for a Channel 4 camer frequency of 67.25 MHz. For
currents are switched at the appropriate RF frequency
Channel 3 operat1on, the resonant frequency should
in 012 through 015. The output signal current is presented
be 61.25 MHz (C = 75 pF, L = 0.1 iJH). Resistors R4 and
at pin 12.
R 5 are chosen to prov1de an adequate amplitude of
Transistors 036, 041 and resistors R44, R4 7 provide
sw1tching voltage, whereas R6 :s used to lower the max'-
a highly stable voltage reference for biasing current sources
mum de level of switch.ng voltage below Vee. thus
043, 034,035, and 011.
preventing saturation withm the IC
Compos1te Luminance and Sync should be de coupled
to Luminance Input, pin 9. This signal must be with;n
MC1372 APPLICATION INFORMATION
the Luma Input Dynamic Range to insure lineanty.
Since an increase in de voltage applied to pm 9 reswts
Chrominance Oscillator
in an increase in RF output, the input s1gnal should
The oscillator is used as a clock signal for drivmg
have positive-going sync to generate an NTSC compatible
associated external circuitry, in addition to providing a
signal, As long as the input s1gnal is pos1tive, over-
switching signal for the chroma modulators. The IC uses
modulation is prevented by the integrated c1rcuit.
an external crystal in a Colpitts configuration, as shown
Chrominance information should be ac coupled to
in Figure 5. Resistor R 1 provides current limiting to
Chrominance Input, pin 10. This pm is internally con·
reduce the signal swing. Capacitor C2 is adjusted for
nected to a resistor div1der consisting of a series 300
the exact frequency desired (3.579545 MHz).
ohms and a shunt 500 ohms resistor. The input impedance
In some applications, the duty cycle of the clock signal
is thus 800 ohms, and a coupling capacitor should be
at pin 1 must be modified to overcome gate delays in
appropriately chosen.
3-8
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