I wonder what is the min. frequency hopping time of hmc833lp6ge or is there any calculator to give min. freq. hopping time because the calculator in hittite.com didnt work
Settling time can be <<100us. However, this depends on the system requirements, such as:
settling accuracy (+/-Hz or +/-degrees);
spectral requirement (phase noise);
channel frequencies (or channel spacing);
All have an effect on the achievable settling time.
In general, time for a PLL to settle after a frequency change (switching time) is determined by the loop bandwidth and phase margin. A wider loop BW provides shorter settling time. A higher phase margin exhibits longer settling time (however, care must be exercised to ensure the phase margin is not too low (~45degrees typically minimum) otherwise PLL instability can result). Loop BW and phase margin are design parameters chosen by the PLL system designer and are not determined by the PLL device.
In addition, the definition of ‘settling’ accuracy effects the settling time (+/-Hz or +/-degrees of target frequency or phase). The PLL will take a longer time to achieve a higher settled accuracy. The settling accuracy definition is dictated by the customer’s application.
Depending on these parameters (loop BW, phase margin and settling accuracy) the PLL settling time can be roughly estimated with this crude ‘rule-of-thumb’:
~10/(LoopBW) to ~20/(LoopBW)
where LoopBW is in Hz and time in seconds.
AD provides a free modeling tool, SimPLL which can be used to estimate the settling time. As with all such tools, settling time should be confirmed through measurement.
In the case of the HMC833 Wideband RF PLL+VCO (and all the other Wideband, Triband & Narrowband RF PLL+VCO products in this family) there is another consideration when performing a frequency change. This family of devices use a ‘switched capacitor’ tank circuit in the VCO. There are 5 binary weighted capacitors that can be switched into the tank circuit under software control to change the nominal resonant frequency of the VCO. The PLL has a built-in state machine that automatically toggles through the switch settings and measures the frequency to determine which is optimum for the programmed frequency. This state machine is referred to as VCO Auto-calibration. For the Wideband PLL+VCO devices (HMC829, HMC830, HMC833. HMC834) there are actually 4 VCO’s, each with 5 switched capacitor. Each switch capacitor sub-band is ~30MHz or more wide. The VCO auto-calibration function is initiated when Reg04h (Fractional mode) or Reg03h (Integer mode) is written. The VCO Auto-calibration feature is describe in this FAQ: https://ez.analog.com/docs/DOC-11784 starting on page 6.
For a typical HMC833 configuration, the VCO Auto-calibration takes ~40us. At the end of this period, control of the VCO Vtune input is relinquished to the PLL CP output and the PLL+VCO exhibits the normal PLL pull-in and settling behavior time, as determined by the loop dynamics (loop bandwidth and phase margin).
The total switching time to change frequencies would be the sum of the VCO Auto-calibration time plus the PLL settling time. For application requirements with slow ~1ms or longer switching time, the VCO Auto-calibration is recommended. For shorter, <<1ms switching time, a manual VCO calibration technique should be applied. A manual VCO calibration implementation can result in a switching time of <100us for reasonable loop bandwidth configurations (~100kHz). Manual VCO calibration is discussed in detail in this application note: http://hittite.com/content/documents/application_notes/Fast_Frequency_Hopping_Application_Note.pdf
DOny thank you very very much for your very very detailed answer ..
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