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Problems With ADF4350 in 2.2-4.4 GHz band

Question asked by Fabrice on Oct 22, 2012
Latest reply on Nov 13, 2012 by icollins


I sometime have problems of lock with ADF4350, but only in the 2.2 to 4.4 GHz band. All other band are working fine.

My design is a wideband synthesizer module using following configuration : 20 MHz ref, PFD = 4 MHz, Fractional N mode, MOD = 4000 to get 1kHz step. MUX configured to get analog Lock.

The problem is that with some chips, I can only get lock on multiples of 4MHz (ie when FRAC = 0 ). Other frequencies lose lock.

In divided bands, there is never any problem !

Software is good, because some chips work ! Communication with chip also, Filter is designed with AdiSimPLL . loop frequency is 20 kHz.

Rset=5.1 k. Icp = 0.94 mA. low noise mode. No fast lock.

Could it be due to variations of Kv over samples ? But why does it work in low bands ?

Is output sensitive to impedance, leading to lock loss in some cases ? Could it improve to change attenuator setting ?

Output is connected to Vvco with 50 R for wideband design.


Thanks in advance for your help.

Best regards,