rf - FM Quadrature detector - is it the best choice

My input is an FM carrier of 80.00MHz. It is FM modulated with 625kbpsec data. The deviation from carrier is about +/-700kHz. The data never spends more than about 38us in a low state or high state i.e. it is scrambled. Carrier is frequency locked using a PIC and a PLL (ADF4111 from memory but this isn't too important other than to say the varactor that "centres" the frequency is fed from a much slower signal than even the lowest data might produce). Please ask if I've forgotten anything relevant.

The above are all givens.

I'm considering using FM quadrature detection - is this the best choice given that I can't alter the transmitter design (well maybe not this month anyway!!).

EDIT - March 21st - the answer below about counting the cycles stirred thoughts and it provoked me to consider using a high-speed Exclusive or gate as an alternative to the conventional mixer circuit within the heart of the quadrature detector. It would still require a resonant 90º phase shift circuit and simple amplitude limiting so, is this a better choice? Options

1. Conventional Quadrature Detector


2. Quad detector using an exclusive or gate


3. Cycle counting techniques


4. A PLL (I've added this but i can't see a decent way of doing it though somebody may)

If one of the above is the best technique, an answer that adequately justifies it gets the nod from me!

Answer

So I've done some research since I have a similar problem and everything leads me to fully integrated quadrature demodulators like LT5517 with a good NCO if you need AFC. All digital systems with direct sampling might have even better noise performance especially if you use oversampling (source) but they have a detection delay, so your application should tolerate this delay if you want to use this method. Search for FPGA or DSP FM demodulators, there are plenty of articles. The best solution for data transmission I've found so far are specialized transceivers with interference resistance like AD9364, but those come in 144-LFBGA and cost $210 per chip. See this article for more info.

If you need a simple and decent demodulator, conventional quadrature demodulator has the best noise performance if you use high quality parts for it.