Monolithic stereo decoder with balanced decoder operation

Claim 1

In a decoder for deriving first and second stereophonically related audio frequency signals from a composite signal including frequency components in the form of the sidebands of a difference combination of said first and second audio frequency signals amplitude modulated on a suppressed carrier wave of given frequency, a sum combination of said first and second audio frequency signals lying in a frequency band lower in frequency than said sidebands and separated therefrom by a frequency gap, and a pilot signal at a frequency equal to one half that of said suppressed carrier wave and which lies in said frequency gap, said decoder comprising means for reconstituting said suppressed carrier, means for detecting the presence of a suitable stereo signal, and means for deriving said first and second stereophonically related audio frequency signals from said composite signal in response to an indication from said detecting means that a suitable signal is present and under the control of said reconstituted suppressed carrier, an input circuit for said decoder for receiving said composite signal and establishing a DC voltage for combining therewith, said input circuit having first and second output channels responsive to the combined signal and means for removing the composite signal from said second channel such that a DC voltage-balanced composite signal including said composite signal at said DC voltage level on said first channel and said DC voltage on said second channel, is applied to said reconstituting means, the detecting means and the deriving means by said first and second channels for balanced linear operation of said decoder.