The $${\rm I}$$-$$V$$ characteristic of an $$LED$$ is

A diode detector is used to detect an amplitude modulated wave of $$60\% $$ modulation by using a condenser of capacity $$250$$ picofarad in parallel with a load resistance $$100$$ kilo $$ohm.$$ Find the maximum modulated frequency which could be detected by it.

Truth table for system of four $$NAND$$ gates as shown in figure is:

The combination of gates shown below yields