Overview: Freescale Semiconductor Data Sheet Document Number: MC44BC375U Rev 3, 8/2006 PLL Tuned VHF (Channel 3 / 4) Audio / Video Modulator
The MC44BC375U and MC44BC375UA are audio/video RF modulators for use in VCRs, set-top boxes, and similar devices. They are designed for applications requiring National Television System mittee, NTSC, channel 3 or channel 4, RF outputs. The difference between the two modulators is the RF output power level. The nominal RFOUT level for the MC44BC375U is 76 dBµV (typical) and the RFOUT level for the MC44BC375UA is 80 dBµV (typical). A programmable Phase-Locked Loop (PLL) tunes the modulator, and the desired channel 3 or 4 frequency isselected using the external package pin, Channel Selection (CHS). No external tank circuit ponents are required, reducing the sensitivity of the PCB design and the need for external adjustments. The PLL obtains its reference from a 4.0 MHz crystal oscillator. The modulators incorporate a sound subcarrier oscillator and use a second programmable PLL to derive subcarrier frequencies. The 4.5 MHz or 5.5 MHz sound carrier frequency is selectable via the package pin, Sound Frequency Selection (SFS). The Picture to Sound subcarrier ratio is also selectable by the pin, Picture to Sound Selection (PSS), to choose either a 14 dB or 16 dB ratio. A low-power standby mode is selectable via the pin, Psave/LO, which turns off all internal VCOs and mixers and simultaneously switches ON an output pin, Logic Output Port (LOP), which may be used as an antenna switch driver.
