A simple PLL FM demodulator circuit using IC XR2212 is shown here. XR2212 is a highly stable, monolithic PLL (phase locked loop) IC specifically designed for communication and control system applications. The IC has 0. 01 Hz to 300KHz frequency range, 4. 5 to 20V operating voltage range, 2mV to 3Vrms dynamic range, high temperature range, TTL / CMOS
compatibility and adjustable tracking range. The operating of a PLL FM demodulator is incredibly simple to know. The input FM signal and the output of the VCO is applied to the part detector circuit. The output of the part detector is filtered employing a low pass filter, the amplifier and then used for controlling the VCO. When there`s no carrier modulation and the input FM signal is in the center of the pass band (i. e. carrier wave only) the VCO`s tune line voltage are going to be at the middle position. When deviation in carrier frequency happens ( that means modulation occurs) the VCO frequency follows the input signal so as to keep the loop in lock. As a result the tune line voltage to the VCO varies and this variation is proportional to the modulation done to the FM carrier wave. This voltage variation is filtered and amplified in order to get the demodulated signal.