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MC44CC373CAS Datasheet(PDF) 5 Page - Freescale Semiconductor, Inc |
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MC44CC373CAS Datasheet(HTML) 5 Page - Freescale Semiconductor, Inc |
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5 / 28 page  Digital Home Freescale Semiconductor 5 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 10 20 30 40 50 60 0 64 TE1 24 28 44 TIMEINµS. 7/10 3/10 TE2 4.75 μs |
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