Hello
I have the CDCE925 device operating in SSC mode (using 0.5%) - what I would like to know is what is the actual modualtion rate of the SSC?
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Hello
I have the CDCE925 device operating in SSC mode (using 0.5%) - what I would like to know is what is the actual modualtion rate of the SSC?
About SSC the SSC sweep frequency depends on the VCO frequency and the “VCO frequency range” selected. (ie. VCO frequency range for PLL1 is set in address 1Bh bits 1:0)
When frequency range selected is fvco<125MHz (bits 1:0 set to 00b) the modulation frequency is (fvco/3200)
When frequency range selected is 125MHz<fvco<150MHz (bits 1:0 set to 01b) the modulation frequency is (fvco/4000)
When frequency range selected is 150MHz<fvco<175MHz (bits 1:0 set to 10b) the modulation frequency is (fvco/4960)
When frequency range selected is 175MHz<fvco (bits 1:0 set to 11b) the modulation frequency is (fvco/5600)
The above is valid for all SSC configuration but for the 0.25 center spread and 0.5 down spread. In this case the formulas are slightly different:
When frequency range selected is fvco<125MHz (bits 1:0 set to 00b) the modulation frequency is (fvco/3410)
When frequency range selected is 125MHz<fvco<150MHz (bits 1:0 set to 01b) the modulation frequency is (fvco/4185)
When frequency range selected is 150MHz<fvco<175MHz (bits 1:0 set to 10b) the modulation frequency is (fvco/5115)
When frequency range selected is 175MHz<fvco (bits 1:0 set to 11b) the modulation frequency is (fvco/5735)
Please find in the excel sheet (please enable macros when you load it) more information. There you can enter a value for the VCO frequency in the orange cell and the SSC modulation frequency updates. In blue is the recommended frequency range for the introduced VCO frequency.
Different VCO ranges are only controlling 6138.SSCCDCE9xx.xls2235.SSCCDCE9xx.xlsthe SSC modulation frequency.
Best regards,
MJ