MC44BC374T1D FREESCALE [Freescale Semiconductor, Inc], MC44BC374T1D Datasheet - Page 17

• Manufacturer Part Number: MC44BC374T1D
• Description: PLL Tuned PAL/NTSC UHF and VHF Audio/Video High Integration Modulator IC
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

13.3.1 STBY Pin Levels
A pull down resistor may be used on STBY pin in order to force an “high impedance” condition into a LO
state (i.e. standby mode condition).
13.4 Transient Output Inhibit
To minimize the risk of interference to other channels while the UHF PLL is acquiring a lock on the
desired frequency, the Sound and Video modulators are turned OFF for each of the following three cases:
There is a time-out of 263ms until the output is enabled. This lets the UHF PLL settle to its programmed
frequency. During the 263ms time-out, the sound PLL current source is set to 10
locking time. After the 263ms time-out, the current source is switched to 1
loop filter components, to ensure the loop transient does not exceed this delay.
For test purposes, it is possible to disable the 263ms delay using Test Mode1–State1.h.
13.5 Video Section — Peak White Clip
The modulator requires:
This signal is AC-coupled to the video input where the sync tip level is clamped.
The video signal is then passed to a Peak White Clip circuit. The PWC circuit function is to soft-clip the
top of the video waveform if the “sync tip amplitude” to “peak white clip” goes too high. This method
avoids carrier over-modulation by the video.
Clipping can be disabled by software.
13.6 Sound Section
The multivibrator oscillator is fully integrated and does not require any external components. An internal
low-pass filter and matched structure give a very low harmonics level.
The sound modulator system consists of an FM modulator incorporating the sound subcarrier oscillator
The audio input signal is AC-coupled into the amplifier, which then drives both types of modulator.
The audio pre-emphasis circuit is a high-pass filter with an external capacitor and an internal resistor
(100kOhms). The recommended capacitor value (470pF) is for BG standard; time constant is 50
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Power-ON from zero (i.e., all Vcc is switched from 0V to 5V).
UHF oscillator power-ON from OFF state (i.e., OSC bit is switched from 0 to 1)
STBY pin switched from LO state to HI state
A composite video input with negative going sync pulses
A nominal level of 1Vp-p
Modulator Mode
STBY pin state
STBY pin level
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high impedance
MC44BC374T1 Technical Data
Normal
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+5V or
HI
Standby
LO
0V
µA
. Use care when selecting
µA
typical to speed up the
Modulator Operation
µs
.