IQ demodulator PFD

Hi,
With an IQ demodulator (lt5515) and a continuos RF(2->2.2ghz) and LO input,
I can tell if the RF is higher or lower then the LO by testing if Q leads I,
and a fairly crude instantaneous phase diference too by mixing them with a
dc offset added to one.

However what I realy want to do is to tell if the RF is higher or lower than
LO+IF(455khz)
and have an instantaneous phase difference.
I assume if I mix each of the above IQ signals with IF in a IQ modulator
this will let me acomplish this,
is there an easy way to implement this ?

I wish to use this to lock the LO.
I know there are other ways to lock a LO but im looking into this way,
as i need to generate the IQ signals anyway.

Colin =^.^=


.

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