mc44353 Freescale Semiconductor, Inc, mc44353 Datasheet - Page 10

• Manufacturer Part Number: mc44353
• Description: Multi.standard Pal/ntsc Modulator
• Manufacturer: Freescale Semiconductor, Inc

Test Pattern Generator
switched in under bus control to permit a TV receiver to easily
tune in to the modulator output. The pattern consists of two
white vertical bars on a black background and a 976 Hz audio
test signal.
MODULATOR SECTION
Video Input–Clamp and Peak White Clip
negative going sync pulses and a nominal level of 1.0 V pp .
This signal is ac coupled to the video input where the sync tip
level is clamped.
whose function is to soft clip the top of the video waveform if
the amplitude from the sync tip to peak white goes too high.
In this way over-modulation of the carrier by the video is
avoided.
Sound Subcarrier Modulator
incorporating the sound subcarrier oscillator, and an AM
modulator. The audio input signal is ac coupled into the
amplifier which then drives the two types of modulator. In
order to provide the accuracy needed for sound subcarrier
f r e q u e n c i e s , t h e s o u n d o s c i l l a t o r c o n s i s t s o f a
phase/frequency locked loop. An external LC tank circuit is
required, and the oscillator frequency is controlled by varicap
tuning diodes. The resulting oscillator frequency is divided
down by a divider whose ratio can be controlled via the bus.
A phase/frequency comparator is then used to compare this
frequency with a reference frequency (Fref 2), obtained from
the main PLL Section. The resulting error voltage is used to
control the varicap. To allow all tuning voltage to be derived
from V CC , a hyper–abrupt type of tuning diode is required to
cover the necessary capacitance range. If only a single
sound subcarrier frequency is being used, for example for
PAL only or NTSC, then a less abrupt varicap diode may be
used. The sound phase frequency comparator also requires
an external loop filter.
6.0 and 6.5 MHz, selectable via the bus. For all applications
except system L, the subcarrier is frequency modulated with
the audio signal. For system L, amplitude modulation is
employed. The level of audio at the input needed to give the
10
0
A simple test pattern is generated on the IC which can be
The modulator requires a composite video input with
The video signal is then passed to a peak white clip circuit
The sound modulator system consists of an FM modulator
The oscillator provides subcarrier frequencies of 4.5, 5.5,
TE1
TE2
Figure 14. TPSG Typical Video Waveform
10
20
24
28
Time in S
30
40
44
7/10
MC44353 MC44354 MC44355
50
3/10
60
64
maximum permissible modulation depth (50 kHz FM
deviation, 85% AM depth), may be adjusted under bus
control.
UHF Oscillator
450 to 860 MHz. The oscillator drives an external LC tank
circuit differentially, and is tuned by a varicap diode. The
varicap tuning voltage, as described in an earlier section, is
provided from an on chip operational amplifier and external
filter arrangement which is controlled by the PLL Section of
the chip. The UHF frequency thus generated is used by the
modulator as the TV channel carrier frequency.
Video Modulator and Sound Mixer
1. composite video;
2. the selected sound subcarrier I 2 C frequency;
3. the UHF carrier frequency at the selected channel;
4. the test pattern generator waveform.
composite video input and the on chip test pattern generator.
The video and sound inter-carrier are used to amplitude
modulate the UHF carrier. Negative modulation is used,
except in the case of System L where positive modulation is
used.In this part of the circuit, the video modulation depth and
the sound to picture carrier ratio may be programmed under
bus control. In system L mode the video modulation depth
has the same range, but may extend to higher percentage
values.
RF O/P Buffer
section is fed to an emitter follower output stage, capable of
driving a terminated line. This output is provided with a
separate V CC pin in order to avoid large circulating currents
on the IC. It can provide at the output typically 84 dB V of
signal across a 75
Transient Output Inhibit
while the UHF PLL is acquiring lock on the desired frequency
at Power-on, the UHF output stages are turned off for each
power-on from zero and from standby mode. There is a
timeout of 263 ms until the output is enabled. This allows the
PLL to settle on its programmed frequency. Care must be
taken therefore in determining the loop filter components so
that the loop transient does not exceed this delay.
Data Retention
frequency and control bits information. The circuit can retain
this information at power down if a suitable V CC is supplied.
V CC Mod. The 5.0 V current in data retention is approximately
500 A. Note that the voltage source on this pin must be able
to supply a much higher current in normal operation (typically
12 mA).
V CCA pin voltage drops below approximately 3.0 V.
The UHF oscillator is designed to operate over a range of
This section of the circuit accepts as inputs:
Selection is made via the control bus between the
The TV signal generated in the video modulator and mixer
To minimize the risk of interference to other channels
The circuit contains 4 bytes of memory holding the last
The Standby V CC of nominal 5.0 V must be applied to pin
The circuit will enter into Data Retention Mode when the
MOTOROLA ANALOG IC DEVICE DATA
load.