XR2211 Linear FM Detector

This is a linear FM detector circuit. This circuit usually is used in telemetry applications and wide range of analog communications. The main part of this circuit is a XR-2211. This circuit has an external buffer/amplifier that is needed due to the high-impedance output at pin 11 of XR-2211. This circuit also has a post-detection filter Rf/Cf. This circuit produce demodulated output. Here is the  schematic diagram of the circuit:

As the buffer/amplifier this circuit uses any noninverting unity gain opamp. The gain of this circuit is determined by following equation:
Vout=R1 VR/100 R0 volts/% deviation, where VR is the internal reference voltage (V+/2 -650mV). [Circuit’s schematic diagram source: seekic.com]