We found this circuit in the 1990 Philips Databook. The circuit is a commercial application of the decoder in stereo FM radio receivers.
This filter is from the Linear Applications Handbook of the National Semiconductor of 1994....
The circuit shown uses the 741 operational amplifier, but lower noise and higher gain equivalents...
This pulse width modulator is from the SGS Integrated Circuits Manual 1982, the operational can be...