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Replacing ADF4154 with ADF4151 to gain lock detect and fast-lock

Hi,

I have a current prototype design with a ADF4154, the ability to achieve quick settling (<20us) using the fast-lock feature is critical, for production I would like to add a lock detect indication and so am considering a replacement part.

My analysis of the parts with a fast-lock switch and a muxout/LD leads me to the conclusion that my possible choices are:

ADF4193/ADF4196

ADF4158/ADF4159

ADF4150

ADF4151

I liked the look of the ADF4193 with its ultra fast settling time, unfortunately I need an active loop filter to achieve the tuning voltage on my VCO, so I think I have to rule out this part (I've seen the extending the tuning range of the ADF4193 app note).

I discounted the ADF4158/ADF4159 on account of ADIsimPLL 3.43.04 not offering any 'Speedup Type' (I wasn't able to simulate the fast-lock loop)

So that leaves me with the ADF4150 or ADF4151, I can take my RF output from the VCO so not needing 4150's output stage, I think the ADF4151 is most suitable.

Using ADIsimPLL 3.43.04 I can achieve similar performance between my proposed ADF4151 part and my current ADF4154, this is encouraging but I still have a few questions:

  - Are there any pitfalls to my approach of replacing the ADF4154 with the ADF4151?

  - Does the same fast-lock register update sequence apply to the ADF4151 as was in the ADF4154 (i.e. I only need to update the N-divider register to achieve a fast-lock jump)?

  - Out of interest why is it not possible to simulate ADF4158/ADF4159 with fast-lock in ADIsimPLL?

Thanks in advance.

Chris

  • Hi,

    There is a few differencs you should be aware of:

    1)The RF frequency range of ADF4151 goes up to 3.5 GHz, while ADF4154 up to 4.0 GHz

    2) Max PFD of ADF4151 in low spur mode is up to 26 MHz (for low noise mode it is 32 MHz), while ADF4154 has max PFD of 32 MHz for all modes

    3) ADF4151 does not support the combined low noise & spur mode

    4) Maximum charge pump current of ADF4151 is 4.5 mA with Rset = 5.1 k, for ADF4151 it is 5 mA in this conditions

    Using fast lock with ADF4151 is easier than with ADF4154.

    1) ADF4151 has a separate field (CLock Divider Value) in Register 3 for fast lock timer (ADF4151 uses the bit field for modulus and the fast lock timer)

    2) Fast lock feature is set in Register 3 and can be activated/deactivated without writing new N value with ADF4151 - once it is selected in Clock Divider Mode field and the right value of Clock Divider Value is chosen for fast lock timer, fast lock will perform any time the frequency is changed

    That means when using ADF4151 you set the fast lock mode once and then you do not have to perform the sequence every time you wish to use the fast lock feature, as it is in ADF4154.

    Regards

    Grzegorz Wawrzola

  • Fast Lock support has not yet been implemented for the ADF4158 and ADF4159 in ADIsimPLL. The priority was on getting the large selection of ramping and modulation scheme implemented first. These parts do support Fast Lock and the functionality will be implemented in a future version of ADIsimPLL.