Converting Variable Frequency TTL to fixed amplitude sine wave

Hello,
I have a VCO circuit based on 4046 IC that generates TTL that varies with input voltage.
I would like to convert this variable frequency signal to sine wave with fixed amplitude (Bandwidth less than 1MHz).

I tried using an RC or LC filter however , the amplitude varies with the frequency so it ended up with signal similar to AM instead of FM.

Is there an easier method to convert the VCO output TTL signal to sine with fixed amplitude ?
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If not is there a method to compensate for the variation in the amplitude or to damp the signals equally to get a fixed amplitude at the end of the day?

Thank you very much in advance.