MAXIM公司的MAX2112是低成本的直接变换调谐器,它为卫星机顶盒(STB)和VSAT应用而设计,适合8PSK和数字视频广播(DVB-S2)应用.采用宽带I/Q下变换器,MAX2112能把LNB中的卫星信号直接转换成基带.工作频率从925MHz到2175MHz.MAX2112包括LNA和可变增益RF放大器,I和Q下变换混频器,有可编程截止频率的基带低通滤波器以及数控的基带可变增益放大器.解决方案包括MAX2112的主要性能,应用领域和方框图以及典型的应用电路图.

       The MAX2112 low-cost, direct-conversion tuner IC is designed for satellite set-top and VSAT applications. The IC is intended for 8PSK and Digital Video Broadcast (DVB-S2) applications.
       The MAX2112 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 with programmable cutoff frequency control and digitally controlled baseband variable-gain amplifiers.

       Together, the RF and baseband variable-gain amplifiers provide more than 80dB of gain control range. The IC is compatible with virtually all DVB-S2 demodulators.

       The MAX2112 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 MAX2112 is the most advanced DBS tuner available today. The low noise figure eliminates the need for an external LNA. A small number of passive components are needed to form a complete DVB-S2 RF frontend solution. The tuner is available in a very small 28-pin thin QFN package.

       主要特性:

       925MHz to 2175MHz Frequency Range
       Monolithic VCO
       Low Phase Noise: -97dBc/Hz at 10kHz No Calibration Required
       High Dynamic Range: -75dBm to 0dBm
       Integrated Variable BW LP Filters: 4MHz to 40MHz
       Single +3.3V ±5% Supply
       Low-Power Standby Mode
       Multiple 2-Wire Addresses for Multituner Applications
       Differential I/Q Interface
       I2C 2-Wire Serial Interface
       Very Small 28-Pin TQFN Package

       应用:

       DirecTV and Dish Network DBS
       DVB-S2
       VSATs

       图1.MAX2112方框图:

       MAX2112典型应用电路图: