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ADRF6518 and AD9684 Output Common Mode Voltage Issue

Question asked by Ma_Li on Jan 24, 2017
Latest reply on Feb 17, 2017 by jdobler

Hi everyone

I have custom board which include ADRF6518 and AD9684 and I design them DC coupling. I tried to reach recommended common mode voltage for AD9684(2.06 Vcm) but could not reach. Here is my scheamtic There is R43 and R44 for Vocm port and I use 1kohm for R43 and 1 Megaohm for R44 I also removed C360 capacitor. Between AD9684 and ADRF6518 there is 180 MHz low pass ceramic filters. I measure Vocm port 3.1 volt and I measured output of the ADRF6518 and VCM voltage is 1.71 volt. I made this measurement with agilent infinnum 54832D oscilloscope and Agilent 1156A probe. Also we give input of the ADRF6518 sinusoidal signal and in output signal is distorted which picture is below. What should I do to reach 2 Vcm and What cause to distort adrf6518 output signal while amplify it.   




Thansk in advance