I am currently using Hittite’s HMC829 to generate a 4GHz clock using a 100MHz sinusoidal input reference. there seems to be a 400 MHz (@ -92dBm) emission from the chip. is this normal? is there anyway to reduce this further?
I suspect this may be the digital ring oscillator used to generate the timing window for the lock detect function. To verify this, it can be disabled by writing Reg07h=0. Alternatively, if Reg07h[11:10] are switched between 00b & 11b, the observed frequency should be seen to shift as the ring oscillator frequency changes.
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