I use the AD9361 as RF front of the domodulater, it is set in a AGC mode and the Rx LO is 390MHz. The IQ data rate is 50MHz. A 390MHz , -50dBm pure carrier RF with a small frequence offset is fed to the AD9361. When the frequence offset is less than 400Hz. The phase of ADC (both I and Q channel ) output somtimes became discontinue. It does not look like a sine wave. Sometimes it seems jump to the maxim value. But when the offset is higher than 500Hz, the phonomenon disapeared. the ADC output became a pure sine wave again.
What is the problem?