Best way to get resonant frequency

Discussion created by jartigas on May 26, 2016
Latest reply on Jun 3, 2016 by rbrennan

Good morning,


like i said in thread Analog devices equivalent IC for LTC6946-3 , i have a desing with a microwave cavity. Its resonant frecuency is between 800-830 MHz. In my actual desing i´m using ADF4117BRUZ + external VCO + feedback circuit for reading received signal (tied to AD converter), and the emited signal has the same power level always.

For getting resonant frequency, i do the following:


     - By means of SPI, i say to ADF4117 put 800MHz.

     - Wait MUXOUT (pin 14) is ON (Lock detect signal).

     - Read AD converter signal from received signal. (The maximun signal received will be resonant frequency). Fmin.


     - Put ADF4117 to 830MHz.

     - Wait lock detect signal.

     - Read AD converter. Fmax.


     - I divide the Fmax-Fmin interval in 5 parts and put in ADF4117

     - Wait lock detect signal.

     - Read AD converter and save the min. and max. value of each part. And so on untill Fmax-Fmin<0,4 (MHz). Then, this is the resonant frequency. It´s a successive approximations method, but the problem is this method takes a long time (about 150 msg).


In my new design, i wanna use ADF4351 (PLL+VCO), I would like to know if anyone knows another faster method for getting the resonant frequency.


If it´s necessary I can put a regulating power emission circuit.


All suggestions are welcome.

Best regards.