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ADL5385 evaluation board for IQ modulation

Question asked by reduction on Sep 3, 2014
Latest reply on Oct 12, 2014 by THA

Hello all,

I would like to use ADL 5385 evaluation board for amplitude, phase and frequency modulation of RF signal. The center frequency is 300MHz.

1. Does DC signal work as I and Q input? If so, different voltage level of I and Q inputs modulate the phase. (Sorry for this simple question. Our oscilloscope is not working so I cannot check it)

2. For frequency modulation, I observe poor suppression for higher order sidebands as shown in the figure. The parameters follow the manual, with 0.7V for I and Q differential input with a 0.5V DC bias; 600MHz LO at -7dBm. Then I fine tune Vp-p and phase for the I and Q signal respectively to better suppress the sidebands (0.001V and 0.1degree resolution). Generally, the baseband feedthrough and the first sideband is suppressed okay. But we get only ~20dB suppression for higher order sidebands. For comparison, the result without DC bias is attached.

Our goal is to get at least 30dB suppression from this. Any suggestions?