Dear Sir,

1) For the ADF4350, is there a fixed phase difference between RF out A and RF out B?

2) Secondly, the datasheet shown that the quantization noise of the SDM is depends on th2e particular phase word which can be varied to optimize the fractional spurs level on any partificular frequency. How can I determine the value of phase word to achieve that spur optimization for let's say 2.37-2.42GHz.

Thanks,

KL

1) The phase relationship between RFoutA+ and RFoutA- is 180 degrees (RFoutB+ and RFoutB- have the same relationship). But the relationship between RFoutA and RFoutB is not defined. Any efforts at predicting a coherent relationship between the two outputs was unsuccessful.

2) The only way to determine the best phase word for a particular frequency is trial and error, and by measuring with the fractional spur level. Luckily this only has to be done once for each value of FRAC/MOD (that is the value of INT does not matter). Note that the phase word is only loaded to the ADF4350 when R0 is updated.

So in an example where the frequency range is 900 - 960 MHz, PFD = 10 MHz, and the channel spacing is 200 kHz. Then 10 MHz / 200 kHz = MOD = 50. So the optimum phase word needs to be determined for each FRAC value from 1 to MOD-1. These can then be reused for any other frequencies that uses the same values of FRAC/MOD. So we only need 49 values of PHASE for the entire frequency range.