This circuit was obtained in the 1990 Motorola Linear Databook. The circuit uses a 139 series comparator, but other series can be used. The power source need not be symmetric.
This high quality circuit with complementary symmetry was found in an Electronics World of 1966....
Found in a 1991 publication this circuit can be assembled with more modern components. We can use...
This circuit was found in a 90s Electronic Design. The integrated circuits are from that time....