This Schmitt trigger in current mode for frequencies up to 50 MHz was found in a 1969 Motorola manual. Appropriate switching transistors can be used.
The circuit shown is from the Texas Instruments optoelectronics manual, applying to low power...
This circuit was found in a 1968 General Electric documentation. It has an input impedance of 2 M ohms...
This filter that rejects a frequency range determined by the double-T was found in the August 1993...