MC44CC373CAS datasheet(5/28 Pages) FREESCALE

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MC44CC373

UHF OSCILLATOR-VHF RANGE

For VHF range operation, the UHF oscillator can be inter-

nally divided by: 2, 4, 8, or 16. This is accomplished via the

special test mode bits, X2:X0.

NOTE:

The MC44CC373/374 modulators are intended for

UHF operation. Using the digital dividers for VHF

operation will cause additional spurious content in the

RFOUT. Performance specifications for VHF operation

are not provided. The user must provide external

filtering on RFOUT to meet their VHF spurious

requirements.

SOUND SECTION

The sound oscillator is fully integrated and does not re-

quire any external components. An internal low-pass filter

and matched structure provide very low harmonics levels.

The sound modulator system consists of an FM modulator

incorporating the sound subcarrier oscillator. An AM modula-

tor is also included in the MC44CC373/374xxxx devices and

is enabled by the SYSL control bit for use in system L appli-

cations. The audio input signal is AC-coupled into the ampli-

fier, which then drives the modulators.

The sound reference divider is programmed by control bit

SRF, resulting in a reference frequency of 31.25 kHz or

62.5 kHz. The sound subcarrier frequency is selected by con-

trol bits SFD1:SFD0. The subcarrier frequencies are 4.5, 5.5,

6.0 or 6.5 MHz. The power-up default value is 5.5 MHz.

A capacitor is connected to the external pin, PREEM, to

set the pre-emphasis time constant for the application. Infor-

mation on the selection of this filter may be found later in this

document under applications information.

LOGIC OUTPUT PORT (LOP)

The LOP pin controls any logic function. The primary ap-

plications for the LOP are to control an external attenuator or

an external switch, between the antenna input and TV output.

A typical attenuator application with PIN diode is shown in

Figure 3. The LOP pin switches the PIN attenuator depend-

ing on the signal strength of the Antenna Input. This reduces

the risks of intermodulation in certain areas. The LOP can

also be used as an OFF position bypass switch or for other

logic functions in the application.

Figure 3. Typical Attenuator Application with Pin Diode

VIDEO SECTION - PEAK WHITE CLIP

The modulators require the following for proper video func-

tionality:

•

A composite video input with negative going sync

pulses

•

A nominal video level of < 1.14 V

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 soft-clips the top of

the video waveform, if the sync tip amplitude to peak white

clip goes too high. This avoids carrier over-modulation by the

video.

The Peak White Clip level may be set via the Option Con-

trol Register 2, bits PW1:PW0. Clipping can be disabled by

software via bit PWC in the Control register.

TEST PATTERN GENERATOR

The modulators have a simple test pattern generator, that

may be enabled under I2C bus control, to permit a TV receiv-

er to easily tune to the modulator output. The pattern consists

of two white vertical bars on a black background and a 1 kHz

audio test signal.

The video test pattern consists of two signals generated by

the Digital section. One controls the sync pulse circuitry, and

the other controls the luminance circuitry. These signals are

logic levels that drive the video circuitry which creates a com-

posite signal with the proper levels for sync pulses and lumi-

nance as shown in Figure 4.

Figure 4. Test Pattern Generator

LOP pin

Vcc

TV Out

Antenna

Input

TE1

24 28

TIMEINµS.

7/10

3/10

TE2

4.75

μs

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