Hi
I have TI's Excel spreadsheet PLL Calculations.xls to help me calculate Loop filter parameters. When I input the following:
Fc=1.2GHz
P=10 N=12
M=1
Fref = 10 MHz
Ko=70 kHz/V
I get an analyzed Freq out of 14.4GHz, and a 22uF capacitor (c2) a LPW of 360 PM of 24 deg, etc I would expect a lower LBW using a 22 uF capacitor.
What am I looking at and is this the right tool?
Could you explain the fields?
Hello Sara,
let's start by some info about CDCM7005 tools.
you can either use the excel version or a more elaborate stand-alone executable (built using Labview libraries) for loop calculations. the executable is more powerful as it supports 3 types of filters including active filter, and calculates the noise and jitter performance as well by providing input and VCO/VCXO noise profiles. (screen shots are shown below). if you have the corresponding EVM available, this version supports direct device programming.
Still the excel version is good to calculate the LPW and PM as you are trying to do here.
Please keep in mind that you need to
1. Enable the add-ins (you will get a message asking for that when opening the sheet) [Macros and Analysis tool pack], if not sure about that, open the File/Options/Add-Ins and Press the Go Button at the bottom of window and make sure the Add-ins are selected.
2. After changing the PLL settings in the sheet, you need to click the "PLL Recalculation" Button.
Regarding The results you get. I think the 14.4GHz output freq. appears because you probably didn't click on the Recalculation.
The LPW/PM are however correct. Note that the 22uF is C2 which determines the zero not the pole of the loop filter. 22uF results in a zero at 1.54 Hz, low as you predicted, first effective pole is at 172.33Hz, and the third pole is at 19.72 kHz. the combination of the 2nd and 3rd poles along with the loop gain results in the overall 360 Hz LPW you see in the calculation. the C2 is mainly affecting the phase maring and based on the placement can indirectly affect the BW.
For example by reducing R2 to 2kOhm, and keeping 22uF for C2, PM increases to 52 deg, LPW becomes 290Hz, and gain peaking is reduced to a reasonable 1.27 dB.
in summary:
- don't be worried about calculation accuracy, it is reliable.
- make sure you enable plugins, and hit the required buttons in Excel
- it's recommended to use the lab view executable version to enjoy more features.
Kind Regards,
Ahmed
