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Sincronization External/internal reference

Category: Hardware

Hello,

I have an application where I use a 10 MHz reference which will lock a 100 MHz VCXO through an ADF4002 PLL.

The equipment will work with an external reference and additionally, it has an internal 10 MHz reference which will be used as back-up solution when the external reference is not available.

I would need a solution which could act over the control voltage of the internal OCXO reference, so if the external reference fails the ouutput frequency of the 100 MHz VCXO continues being exactly the same when it will lock to the internal reference. If the equipment is switched on without external reference, the output frequency when operating with internal reference must be exactly th frequency configured in factory.

Could you recommend me a circuit to implement this functionality? I have done it in others equipment using and ADF9542 but this solution need an additional OCXO 10 MHz reference to be used as system clok. I am looking fo a solution avoiding this additional system clock.

Thanks in advance for your support and advices.