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Large unexpected modulation in ADL5390-EVAL

Question asked by camacazio on May 5, 2016
Latest reply on Jun 3, 2016 by camacazio

I have an application where an RF 200 MHz source is delivered by VCO (Minicircuits ZOS-200+) into the RFIN_I input of the ADL5390-EVAL board. The Q inputs are terminated, and the I baseband inputs are P: ground and N: to 0.5V. The RFOP, final output, from the eval board shows the central line with frequency-dependent heavy modulation. As frequency is varied, behavior can range from 100 MHz sidebands to densely spaced sidebands of varying height. Behavior is modified by whether or not the Q inputs are terminated or jumpered to 0.5V. 5V supply is provided by a LM7805 regulator, with 10 uF aluminum polarized capacitors. What are possible sources and solutions to this modulation problem?