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MC44BC374T1 Datasheet(PDF) 17 Page - Freescale Semiconductor, Inc
FREESCALE [Freescale Semiconductor, Inc]
MC44BC374T1 Datasheet(HTML) 17 Page - Freescale Semiconductor, Inc
/ 26 page
MC44BC374T1 Technical Data
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:
Power-ON from zero (i.e., all Vcc is switched from 0 V 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
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
typical to speed up the
locking time. After the 263ms time-out, the current source is switched to 1
. Use care when selecting
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–State 1.h.
13.5 Video Section — Peak White Clip
The modulator requires:
A composite video input with negative going sync pulses
A nominal level of 1Vp-p
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
(100 kOhms ). The recommended capacitor value (470pF ) is for BG standard; time constant is 50
STBY pin state
STBY pin level
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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