LMX2594: Phase shift controlling

Hi Amir,

Right we can use MASH_SEED to shift the output phase w.r.t. the reference clock. The phase shift is single direction in an accumulation matter. That is, if we program the same MASH_SEED value 10 times, phase will be shifted 10 times. I expect there will be disturbance to the VCO when we write MASH_SEED, I have not checked this before. I don't have exact response time, but it is related to PLL_DEN setting. The larger PLL_DEN, the longer response time.

Can you accept single direction shift?

then output is not stable during MASH_SEED writing process. I need to move the clock edge right and left and single direction in applicable to us. and having stable clock is critical to the design. do you have any other suggestion?

Hi Amir,

Since the phase shift is performed in the MASH, the disturbance is expected. Currently we don't have a part that can do the phase shift after VCO. 

Hi Noel,

what about reference clock? if we shift it then could we control the output phase without disturbance?

Hi Amir,

PLL will always try to track the input reference clock, any change from the reference clock will reflect on PLL output. If the phase shift in the input is gentle, there should be no disturbance at the output. However, if the phase shift is abrupt, I expect we should see some glitches at the output.

hey Fung,

if we want to sift phase of clock precisely and dynamically,  assume  with in 20ps resolution. what solution do you recommend, pll base or vco?

thanks

Hello Amir, 
I believe what Noel is trying to explain is that the PLL will handle small glitches and adjust the CP accordingly due to the difference in phase but a large abrupt phase difference can trigger a glitch on the output side. 

As mentioned we have phase shift functionality in our devices but it's in one direction only and this phase shift does not occur after the VCO but instead in the MASH engine. 

Regards, 

Vicente