HMC83x PLL+VCO Evaluation Board Drift

HMC829, HMC830, HMC832, HMC832A, HMC833, HMC834, HMC835, HMC983/984, HMC1033, HMC1034

The above HMC PLL+VCO Eval board offers the user flexible reference signal sources.


Mode 1.

Lab equipment 10MHz output phase locked to HMC DUT Eval Board.

These boards use the HMC1031 integer N-PLL and a 50.000MHz +/-150ppm VCXO.

The HMC1031 is a pin selectable INT-N PLL.

It’s used as a jitter attenuator and to phase lock the 50.000MHz VCXO to the user’s 10MHz reference output on their Spectrum/Network Analyzer.

HMC1031 multiplication factor is set by SW1 which by default is x5 mode (10 à 50).

This is the default configuration for these boards and is recommend since if using the on board 50.000MHz reference, the HMC1031 charge pump will force the VCXO’s input high and pull +150ppm (typical).


Mode 2. 

With HMC1031 jitter cleaner not locked to external reference. 

This is the normal operating mode with no connection on J5. 

In this mode the HMC1031 is not locked since there is no reference on J5.  The onboard 50MHz VCXO operates open loop at its maximum frequency –  somewhere around 50.007MHz (150ppm).  

Many users have noted the output frequency not meeting 3Hz accuracy. This is since they haven’t locked the board reference to the measurement equipment.


Mode 3. 

This mode bypasses the HMC1031 and powers down the 50MHz VCXO

The external reference is attached to J5 and applied directly to the HMC833 reference input.

Cxx and Rxx are removed to prevent stubs, and Rxx and Rxx zero ohm resistors are installed to connect the reference signal around the HMC1031.

Note that the reference designators above are board dependent.