Modulator Functionality

MC44BC375/U/J/T Technical Data

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

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

75

µs. 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).

12.8 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 different for each of

the 3 versions.

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

VHF frequencies:

12.9 Selectable Pins

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

Device

Channel

VHF divider

MC44BC375U

CH3 = 61.25Mhz

8

CH4 = 67.25Mhz

MC44BC375J

CH1 = 91.25Mhz

6

CH2 = 97.25Mhz

MC44BC375T

CH13 = 211.25Mhz

3

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com