AY,
Input bias currents can lead to high spurs. In the old days with integer PLLs, it was a big deal, but newer PLLs have much higher phase detector rates and can tolderate much higher bias currents, althouogh uA range is still something to consider…
Sam,
According to the PLLatinum Sim tool ( http://www.ti.com/tool/PLLATINUMSIM-SW , the loop bandwidth is 4.8 kHz and the formulas used to this are in my online PLL book at http://www.ti.com/tool/pll_book . We define the loop bandwidth as the frequency…
Variac,
PLLatinum Sim does model the impact of MASH_SEED on spurs, but not for a numerator of 0 as you say. The impact of MASH_SEED on spurs does not have a simple closed formula, but rather involves finding the sequence and calculating the Fourier…
Andrew,
The concepts used for PLLatinum Sim active filters are discussed in depth in my PLL book at ( www.ti.com/.../pll_book).
For PLLatinum Sim, indeed there is an error in the type A and type B filters and the + and - signs are swapped. I will fix…
Bert,
If you enjoyed my book revision, I encourage you to visit my new revision at http://www.ti.com/tool/pll_book and also the PLLatinum Sim tool that is based on this book
As for this behavior, we saw this in our characterization with the resistor…
Hello Madhu
Here are answeres to your questions:
1) I am not using any primary input ( only a 25Mhz crystal). In the tool after disabling the primary input, if i turn the primary frequency to zero, VCO gives an error. Does this mean that it is necessary…
Teach me,
The pictures would be helpful, but some other things you can do:
1. Be sure to check out our PLLatinum Sim software at www.ti.com/.../PLLATINUMSIM-SW
2. You can check out our online PLL book that discusses PLLs and fractional sprus in depth…
Alex,
I would highly encourage you to read my 5th edition PLL book at ( http://www.ti.com/tool/pll_book ). You can read for free online and I expect the hardcover to be out in a few weeks. This PLL fundamentals document you mention was a training I put…
Alex,
A few strategies we have for Fpd spurs are:
1. In general, lower loop filter bandwidth, helps filtering of out-of-band (offsets higher than loop bandwidth) spurs.
2. Depending on the Fpd frequency, designing 3rd order loop filters also sometimes…
Alber,
No, there really is no other way without using an active device of some sort. Our EVM instructions shows how to do an active filter.
If you really want to avoid the op-amp, then you could use a darlington pair of transistors as shown on page 203…