Frequecy demodulator with high accuracy

Dear guys,

I have to design a frequency demodulator with high accuracy (around 1 Hz), hold range of few kHz and central frequency 400 KHz. I am thinking to use the popular 74HCT297 ADPLL to realize it with a crystal oscillator for I/D clock and large K modulus for the desired bandwidth. Unfortunately, my knowledge about demodulator is limited, what is the frequency resolution achievable by using that? How can I detect the frequency when the PLL is locked?
Many thanks for helping me.

Luc

"a frequency demodulator with high accuracy". Do you mean a very linear FM demodulator? Do you mean some sort of frequency meter?
In general, if you try and phase lock to a FM or PM signal, the output from the phase comparator is the demodulated modulation, which is then removed by the LPF before the amplifier and phase control element that adjusts the lock frequency.
Frank

Take the error voltage from a locked PLO, this is proportional to frequency shift between the output frequency and the reference signal frequency.
The error voltage comes from the phase detector, and it is then filtered (smoothed) to be used as tuning voltage in the VCO. Before the filter it indicates the frequency difference between the two.