Question
What is the charge pump value and how is it set in the ADF4106?
Answer
All our frequency synthesizers are current output devices and are quoted with a
sensitivity of current per radian.
Kd = 2.5mA is the charge pump current setting per 2pi radians (i.e. (2.5/2pi)mA
per radian.
The ADF4106 charge pump current setting is programmed by the current setting
bits in the function latch map (Table 9 on page 15 of datasheet RevD). When the
required frequency is changed the ADF4106 will produce a DC current for a very
short period of time followed by current pulses which reduce in size as lock is
approached. Once lock is detected, the current pulses are too minute to be
measurable.
The loop filter acts to integrate these current pulses into a voltage applied
to the VCO. You can use ADIsimPLL to design the loop filter
(https://form.analog.com/Form_Pages/RFComms/ADISimPll.aspx)