MAX2121全直接變頻L波段調(diào)諧器

　　The MAX2121 low-cost， direct-conversion tuner IC is designed for satellite set-top and VSAT applications. The device directly converts the satellite signals from the LNB to baseband using a broadband I/Q downconverter. The operating frequency range extends from 925MHz to 2175MHz. The device includes an LNA and an RF variable-gain amplifier， I and Q downconverting mixers， and baseband lowpass filters and digitally controlled baseband variable-gain amplifiers. Together， the RF and baseband variable-gain amplifiers provide more than 80dB of gain control range. The device includes fully monolithic VCOs， as well as a complete fractional-N frequency synthesizer. Additionally， an on-chip crystal oscillator is provided along with a buffered output for driving additional tuners and demodulators. Synthesizer programming and device configuration are accomplished with a 2-wire serial interface. The IC features a VCO autoselect （VAS） function that automatically selects the proper VCO. For multituner applications， the device can be configured to have one of two 2-wire interface addresses. A low-power standby mode is available whereupon the signal path is shut down while leaving the reference oscillator， digital interface， and buffer circuits active， providing a method to reduce power in single and multituner applications. The device is the most advanced broadband/VSAT DBS tuner available. The low noise figure eliminates the need for an external LNA. A small number of passive components are needed to form a complete broadband satellite tuner DVB-S2 RF front-end solution. The tuner is available in a very small， 5mm x 5mm， 28-pin thin QFN package.