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CMX970 IF/RF Quadrature Demodulator

Quadrature Demodulator

Typical system application utilising:

CMX970—IF/RF Quadrature Demodulator

CMX998—Cartesian Feedback Loop (CFBL) Transmitter

CMX7861—Programmable Baseband Interface IC

The quadrature demodulator is designed for IF/RF operation and has very low power consumption. Input frequencies in the

range 20 to 300 MHz are allowed. The demodulator system has two gain stages, one before and one after the I/Q

down-converters and the gain elements can be independently controlled. This flexible architecture allows the users to

optimise characteristics depending on their system requirements. Optimum noise figure can be achieved by maximising gain in

first gain stage and minimising gain in the second stage. Intermodulation performance can be optimised by decreasing gain in

the first or second stages. A lower gain in the second gain stage will tend to reduce dc offsets in the output I/Q signal. Further

detailed information on the effects of controlling gain stages is available in the CMX970 datasheet.

CMX970 RF Receiver

‘I’ In

‘Q’ In

Divider

CMX998 CFBL Transmitter

‘I’ Out

Divider

‘Q’ Out

T/R

GPIO

ADC

Clocks

DACs

DSP

Microcontroller

90

PLLs/

VCO

PA