MC44BC374EJB Freescale Semiconductor, MC44BC374EJB Datasheet - Page 16

• Manufacturer Part Number: MC44BC374EJB
• Description: IC MODULATOR ANT BOOSTER 24TSSOP
• Manufacturer: Freescale Semiconductor
• Type: Modulatorr

Specifications of MC44BC374EJB

• Applications: Set-Top Boxes
• Mounting Type: Surface Mount
• Package / Case: *
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Modulator Operation
There is a time-out of 263ms until the output is enabled. This allows the UHF PLL settle to its
programmed frequency. During the 263ms time-out, the sound PLL current source is set to 10µA typical,
to speed up the locking time. After the 263ms time-out, the current source is switched to 1µA.
For test purposes, it is possible to disable the 263ms delay using Test Mode1–State1.h.
12.7 Logic Output Port (LOP)
The LOP pin controls any logic function. The primary applications are to control an external attenuator or
an external switch between the antenna input and TV output. When an external switch is controlled, the
Booster function is not used.
The following figure shows a typical attenuator application with PIN diode. The LOP pin switches the
PIN attenuator depending on the signal strength of the Antenna Input, thereby reducing the risks of
Intermodulation in certain areas. The LOP may also be used as an OFF position bypass switch or for other
logic functions in the application.
12.8 Video Section—Peak White Clip
The modulator requires the following:
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 (PWC) circuit. The PWC circuit function sets 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.
12.9 Sound Section
The multivibrator oscillator is fully integrated and does not require external components. An internal low
pass filter and matched structure provide a very low harmonics level.
The sound modulator system consists of an FM 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 modulators.
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. (50µS time constant.)
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A composite video input with “negative going” sync pulses
A nominal level of 1Vp-p
Use care when selecting loop filter components, to ensure the loop
transient does not exceed the specified delay.
Figure 9. Attenuator Application with PIN Diode
Freescale Semiconductor, Inc.
Antenna
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Input
MC44BC373/374 Technical Data
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LOP pin
Vcc
CAUTION:
TV Out