Maxim MAX2120机顶盒调谐方案

Maxim公司的MAX2120是低成本直接变换硅调谐器，主要应用于机顶盒（STB）和VSAT的QPSK和数字视频广播（DVB-S），DSS和免费的地面接收。MAX2120包括LNA和RF可变增益放大器（VGA），I和Q下变换混频器以及带通滤波器，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。MAX2120可应用于DirecTV和碟形卫星天线的网络DBS，DVB-S，双向卫星系统和卫星信号的免费的地面接收以及VSAT。本文介绍了MAX2120的主要性能，方框图以及典型的应用电路图。

概述：
The MAX2120 low-cost, direct-conversion tuner IC is designed for satellite set-top and VSAT applications. The IC is intended for QPSK, Digital Video Broadcast (DVB-S), DSS, and free-to-air applications. The MAX2120 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 QPSK demodulators.

The MAX2120 includes fully monolithic VCOs, as well as a complete frequency synthesizer. Additionally, an onchip 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 auto*** (VAS) function that automatically ***s 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 MAX2120 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, DBS, or VSAT 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: No Calibration Required
♦ -75dBm to 0dBm High Dynamic Range
♦ 4MHz to 40MHz Integrated Variable BW LP Filters
♦ 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 Thin QFN Package

应用：
DirecTV and Dish Network DBS
DVB-S
Two-Way Satellite Systems
VSATs
Free-to-Air
MAX2120功能方框图：

典型应用电路图：