I'm in the process of learning about radio circuits, and while learning about discriminators I though up an idea! What if you used a Wheatstone Bridge to output the change in voltage with the IF as the input, and a capacitor as the unknown resistance? So that the change in frequency would result in a change in impedance. Looking into the idea I would actually need a Maxwell bridge which is the Wheatstone bridge AC equivalent.

Do you think this could work? How well do you think it would work? Obviously I just came up with this idea and haven't put much thought into response time and stuff like that. Let me know! Would it be less efficient than a slope detector? I sort of doubt it could be better than the PLL discriminator. Thoughts?

 

In principle I think the idea might work with some caveats concerning matters like output linearity, circuit Q & transient behavior. The attachment shows how one might conceptually do it with a Twin-T bridge arrangement. How it would compare with established methods would be a matter of test & measure.
However, I think a basic problem with the concept is that the circuit cannot distinguish whether the instantaneous frequency is above or below the center IF, which would probably be its Achilles' Heel.