GENERAL DESCRIPTION

The AD8348 is a broadband quadrature demodulator with an integrated intermediate frequency (IF), variable gain amplifier (VGA), and integrated baseband amplifiers. It is suitable for use in communications receivers, performing quadrature demodulation from IF directly to baseband frequencies. The baseband amplifiers are designed to interface directly with dual-channel ADCs, such as the AD9201, AD9283, and AD9218, for digitizing and post processing.

The IF input signal is fed into two Gilbert cell mixers through an X-AMP® VGA. The IF VGA provides 44 dB of gain control. A precision gain control circuit sets a linear-in-decibel gain characteristic for the VGA and provides temperature compensation. The LO quadrature phase splitter employs a divide-by-2 frequency divider to achieve high quadrature accuracy and amplitude balance over the entire operating frequency range. Optionally, the IF VGA can be disabled and bypassed.

In this mode, the IF signal is applied directly to the quadrature mixer inputs via the MXIP and MXIN pins.

FEATURES

* Integrated I/Q demodulator with IF VGA amplifier

* Operating IF frequency 50 MHz to 1000 MHz

(3 dB IF BW of 500 MHz driven from RS= 200 Ω)

* Demodulation bandwidth 75 MHz

* Linear-in-decibel AGC range 44 dB

* Third-order intercept

IIP3 +28 dBm @ minimum gain (FIF= 380 MHz)

IIP3 −8 dBm @ maximum gain (FIF= 380 MHz)

* Quadrature demodulation accuracy

* Phase accuracy 0.5°

* Amplitude balance 0.25 dB

* Noise figure 11 dB @ maximum gain (FIF= 380 MHz)

* LO input −10 dBm

* Single supply 2.7 V to 5.5 V

* Power-down mode

APPLICATIONS

* QAM/QPSK demodulator

* W-CDMA/CDMA/GSM/NADC

* Wireless local loop

* LMDS