Maxim MAX2120機頂盒調諧方案

Maxim公司的MAX2120是低成本直接變換硅調諧器，主要應用于機頂盒（STB）和VSAT的QPSK和數字視頻廣播（DVB-S），DSS和免費的地面接收。MAX2120包括LNA和RF可變增益放大器（VGA），I和Q下變換混頻器以及帶通濾波器，能把LNB來(lái)的衛星信號采用寬帶I/Q下變換器傳輸給基帶處理器。工作頻率從925MHz到2175MHz。MAX2120可應用于DirecTV和碟形衛星天線(xiàn)的網(wǎng)絡(luò )DBS，DVB-S，雙向衛星系統和衛星信號的免費的地面接收以及VSAT。本文介紹了MAX2120的主要性能，方框圖以及典型的應用電路圖。

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

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

典型應用電路圖：