Architecture of RF Front End Digital to Analog Converter DAC5687 Baseband Processor Baseband Processor Analog to Digital Converter ADC08200 ADC08200 ADC8369 ADC8369 AD 8347 MGA665P8 TRF3761 FREQUENCY SYNTHESIZER I/Q MODULATOR TRF3703 MwT-17Q3 RF Front End Baseband Section Architecture of RF Front End Tx Ant Rx Ant
Direct Conversion Receiver LO frequency is equal to RF carrier frequency Converts RF signal to Zero frequency and hence called as Zero IF Receiver Simple Low Pass filter is used Image reject filter is not required Well suited for integration whole receiver ON-CHIP.
Equation E1 Shows gain compression with increase in level of input signal and is characterized by 1 dB compression point.
Equation E2 shows that 3 rd order distortion increases as cube of amplitude of the applied signal or 3 times in dB. The amplitude of input signal where IMD and Desired signal are equal is known as IIP3 or Input referred third order intercept point.
The mixer is a non linear device and can be represented by a non linear polynomial of fourth degree to consider up to 3rd order IMD
The coefficients c i for above can be calculated by analyzing the output for known signal. The parameters taken into consideration to compute the model include LO to IF leakage, RF to IF leakage, Third order intercept point IIP3 and Conversion Loss.
The values of c1, c2, c3, c4 are respectively 0.15263, 0.9142, -0.6, 0.0077
The mixer is implemented in Matlab.
LNA and Mixer stages are cascaded and the output at each stage is shown.
Output Obtained from Non Linear Models of LNA & Mixer
Considering two transmissions received at 935, 935.2 MHz with
-25 dBm level of each signal
LNA Input Two Signals at 935 & 935.2 MHZ, -25 dBm each.
Output of LNA The Intermodulation products are observed at 934.8 and 935.2 MHz
Mixer Output 1 Down converted GSM Signal 2 Down converted WiFi Signal 1 2 3 Third Order Intermodulation Products of WiFi and LO 3 4 Third order intermodulation product of LO and GSM signal along with RF to IF leakage 4 5 RF to IF leakage of WiFi 5 6,7 Upconverted GSM and WiFi Signals 6 7