I have an eval for the ADF4371 and I'm using an HMC1031 eval to lock the 100MHz ref to a precision 10MHz OCXO. I am generating an 18GHz LO. As seen here:
The problem here is measured PN at 100Hz offset. With the on-board crystal reference PN @ 100Hz = -87dBc/Hz. With HMC1031 PN @ 100Hz = -67dBc/Hz.
Notable design parameters:
- HMC1031 Loop BW set to 10Hz as outlined in the spec sheet page 12. www.analog.com/.../hmc1031.pdf
- 100MHz VCXO, CVHD-950, CMOS output
- The measure slew rate from the HMC1031/CVHD-950 better than on board 100MHz reference.
Thanks in advance!
Hi Chris,The Flicker FOM of HMC1031 is -252dBc/Hz. This gives -112dBc/Hz @ 100Hz offset @ 100MHz output. PNFLICK = Flicker FOM + 20log(fVCXO) − 10log(fOFFSET)If this is transferred to 18GHz;-112…
Are you able to measure PN of CVHD-950 alone and with HMC1031? Is there any notable difference?
I am not able to measure the PN of the CVHD-950 or the on-board CCHD-575-50-100.000 due to dynamic range limitations of the test equipment. I would need a much better SA than I have here to measure the PN of those units.
Can you try to isolate the CVHD-950 from HMC1031 and check the result?
I see about 5dB improvement possibly a little more. The open loop VCO is drifting even though the Vctrl is tied to ground. It looks like the signal tracker is not able to keep up. Anyway, there is some improvement.
Hi Chris,The Flicker FOM of HMC1031 is -252dBc/Hz. This gives -112dBc/Hz @ 100Hz offset @ 100MHz output. PNFLICK = Flicker FOM + 20log(fVCXO) − 10log(fOFFSET)If this is transferred to 18GHz;-112 -20log(18G/100M) = -67dBc/Hz.If I did not make any mistake in calculations, math says that your measurement is very accurate. The contributions from other sources (OCXO, VCXO, PLL floor FOM, loop filter) are not significant.When using CVHD in open loop, I would also expect to see something close to -87dBc/Hz. But it is possible that the instrument cannot track the signal as you advised. Perhaps you can try to force Vtune to a mid-level instead of connecting it to GND. Min and max levels might be problematic. Regards,Kazim