MC44BC373C Datasheet, PDF (20/30 Pages) Motorola, Inc – PLL Tuned UHF and VHF Audio/Video High Integration Modulator

Modulator Description ^{Freescale Semiconductor, Inc.}
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
(100kOhms). The recommended capacitor value (470pF) is for BG standard; time constant is 50µS.
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.
TE2
7/10
3/10
TE1
0
10
20 24 2830
40 44 50
60 64
TIME IN µS.
Table 1. Test Pattern Generator
MC44BC373C/374C Technical Data
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