A circuit arrangement for detecting and recognizing the type of optical recording medium being scanned, in which a high pass filter is connected in series with a rectifier. The high pass filter receives a data signal containing information stored in the recording medium. A low pass filter has an input...http://www.google.com.au/patents/US5202874?utm_source=gb-gplus-sharePatent US5202874 - Circuit arrangement for identifying the type of an optical record carrier
