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MC44BC375UAFCR2

MC44BC375UA PLL Tuned VHF Audio/ Video High Integration IC (Channel 3 and 4 80 dBµV RF Level)

Freescale Semiconductor 

Freescale Semiconductor, Inc.Modulator Functionality

The video signal is then passed to a peak white clip circuit 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. The clipping function is always engaged.

13.7 Sound Section

The multivibrator oscillator is fully integrated and does not require any external component. An internal

low pass filter and matched structure give 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 the modulator.

The audio pre-emphasis circuit is a high-pass filter with an external capacitor C1 and an internal resistor

(100kOhms typical). The recommended capacitor value (750pF) is for M/N standards; time constant is

75µs. It is 470pF for B/G standards (50µs).

Audio bandwidth specification is for 50Hz to 15Khz range, with pre-emphasis circuit engaged. Without

this pre-emphasis circuit, it is possible to extend the audio bandwidth to the high frequencies as there is no

internal frequency limitation (stereo application).

13.8 PLL Section — Dividers

The reference divider is a fixed divide by 128 resulting in a reference frequency of 31.25Khz with a

4.0Mhz crystal. The 31.25Khz reference frequency is used for both UHF and Sound PLLs.

The prescaler is a fixed divide by 8 and is permanently engaged. The VHF divider is also a fixed divide by

8.

The programmable divider’s division ratio is controlled by CHS pin voltage in order to get the channel 3 or

channel 4.

13.9 Selectable Pins

Pins CHS, PSS, SFS are internally pulled up to 5V.

MC44BC375UA Advance Information

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