US Patent 3,475,623:
Electronic High-pass and Low-pass Filters Employing the Base-to-Emitter Resistance of Bipolar Transistors
“I have been collecting copies of Moog patents, those invented by Robert Moog and as well as those assigned to Moog Music, Inc., and the synthesizer-related patents of Norlin Music, Inc., the company that purchased Moog Music. I present them here along with some hopefully entertaining commentary.”
– J. Donald Tillman
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