GSM 3 V Transceiver IF Subsystem
Rochester Electronics is the only authorized source of Analog Devices' products that have previously been discontinued or have become obsolete. Product availability should be checked directly with Rochester Electronics.
The AD6432's receive signal path is based on the proven architecture of the AD607 and the AD6459. It consists of a mixer, gain-controlled amplifiers, integrated roofing filter and I/Q demodulators based on a PLL. The low noise, high-intercept variable-gain mixer is a doubly-balanced Gilbert-cell type. It has a nominal -13 dBm input-referred 1 dB compression point and a 0 dBm input-referred third-order intercept.
The gain-control input accepts an external control voltage input from an external AGC detector or a DAC. It provides an 80 dB gain range with 27.5 mV/dB gain scaling, where the mixer and the IF gains vary together.
The I and Q demodulators provide inphase and quadrature baseband outputs to interface with Analog Devices' AD7015 and AD6421 (GSM, DCS1800, PCS1900) baseband converters. An onboard quadrature VCO, externally phase-locked to the IF signal, drives the I and Q demodulators. The quadrature phase-locked oscillator (QPLO) requires no external components for frequency control or quadrature generation, and demodulates signals at standard GSM system IFs of 13 MHz, or 26 MHz with a reference input frequency of 13 MHz; or, in general, 1X or 2X the reference frequency. Maximum reference frequency is 25 MHz.
This reference signal is normally provided by an external VCTCXO under the control of the radio's digital signal processor. The transmit path consists of an I/Q modulator and buffer amplifier, suitable for carrier frequencies up to 300 MHz and provides an output power of -17.5 dBm in a 50 Ohm system. The quadrature LO signals driving the I and Q modulator are generated internally by dividing by two the frequency of the signal presented at the differential LO port of the AD6432. In both the transmit and receive paths, onboard filters provide 30 dB of stopband attenuation.
The AD6432 comes in a 44-lead plastic thin quad flatpack (TQFP) surface mount package.