MC44BC373C/374C Technical Data

Modulator Description

13.11 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 the following two types:

•

An FM modulator incorporating the sound subcarrier oscillator

•

An AM modulator (MC44BC373C only)

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

µS.

13.12 Test Pattern Generator

The IIC generates a simple test pattern, which can be switched under bus control to permit a TV receiver to

easily tune to the modulator output. The pattern consists of two white vertical bars on a black background

and a 976Hz audio test signal.

Table 1. Test Pattern Generator

10

20

30

40

50

60

0

64

TE1

24 28

44

TIME IN µS.

7/10

3/10

TE2

Freescale Semiconductor, Inc.

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