Maxim公司的MAX2112是低成本直接变换硅调谐器，主要应用于机顶盒（STB）和VSAT的8PSK和数字视频广播（DVB-S2）。MAX2112能把LNB来的卫星信号采用宽带I/Q下变换器传输给基带处理器。工作频率从925MHz到2175MHz。MAX2112可应用于DirecTV和碟形卫星天线的网络DBS，DVB-S2以及VSAT。本文介绍了MAX2112的主要性能，方框图以及典型的应用电路图。
详情请见MAX2112数据表：下载
概述
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
♦ 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功能方框图：
图2。MAX2112典型应用电路图。
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