Linear LTC6603可编程低通滤波方案

Linear公司的LTC6603是双路匹配的可编程低通滤波器,主要用于通信领域中的接收器和发送器. LTC6603的选择性,9阶线性相位,两路间的1.5度相位匹配以及动态范围特性,使它能在许多通信系统用作滤波器如发送器的I和Q通道.可编程的带宽高达2.5MHz,可编程增益0dB/6dB/12dB/24dB. LTC6603的工作电压2.7V到3.6V,输入电压范围从0V到5.5V,噪音为–145dBm/Hz,200kHz的失真为-75dBc.本文介绍了LTC6603的主要特性,方框图,典型应用电路以及电流控制时钟频率, AC耦合输入电路图, 主/从时钟配置方框图, 并行和SPI时钟控制框图和用于WCDMA的直接变换解调器以及I和Q基带滤波器电路图.

The LTC6603 is a dual, matched, programmable lowpass filter for communications receivers and transmitters. The selectivity of the LTC6603, combined with its linear phase,
phase matching and dynamic range, make it suitable for filtering in many communications systems. With 1.5° phase matching between channels, the LTC6603 can be used in applications requiring pairs of matched filters, such as transceiver I and Q channels. Furthermore, the differential inputs and outputs provide a simple interface for most communications systems.

The sampled data filter does not require an external clock yet its cutoff frequency can be set with a single external resistor with an accuracy of 3.5% or better. The external resistor programs an internal oscillator whose frequency is divided prior to being applied to the
filter networks.

This allows up to three cutoff frequencies that can be obtained for each external resistor value, allowing the cutoff frequency to be programmed over a range of more than six octaves. Alternatively, the cutoff frequency can be set with an external clock. The filter gain can also be programmed to 1, 2, 4 or 16.

The LTC6603 features a low power shutdown mode that can be programmed through the serial interface and is available in a 24-pin 4mmx4mm QFN package.

主要特性:

Guaranteed Phase and Gain Matching Specs
Programmable BW Up to 2.5MHz
Programmable Gain (0dB/6dB/12dB/24dB)
9th Order Linear Phase Response
Differential, Rail-to-Rail Inputs and Outputs
Low Noise: –145dBm/Hz (Input Referred)
Low Distortion: –75dBc at 200kHz
Simple Pin Programming or SPI Interface
Set the Max Speed/Power with an External R
Operates from 2.7V to 3.6V
Input Range from 0V to 5.5V
4mm 4mm QFN Package

应用:
Small/Low Cost Basestations:
IDEN, PHS, TD-SCDMA, CDMA2000, WCDMA, UMTS
Low Cost Repeaters, Radio Links, and Modems
802.11x Receivers
JTRS



图1.LTC6603典型应用



图2.LTC6603方框图



图3.LTC6603电流控制时钟频率



图4.LTC6603 AC耦合输入电路图



图5.两个LTC6603的主/从时钟配置方框图



图6.LTC6603并行时钟控制框图



图7.LTC6603 SPI时钟控制框图



图8.采用LTC6603的直接变换解调器以及I和Q基带滤波器电路图(fcutoff=1.92MHz,UTMS WCDMA)