Simple Frequency Doubler

Using just a few discrete components and two inverters, it is possible to build a simple TTL square wave frequency doubler for signals up to about 100 kHz. The input signal is applied to the differentiating circuit R1-C1. This converts the rising edge of the square wave into a positive pulse and the falling edge into a negative pulse. The inverter IC1a (you could use a NAND or NOR gate with the inputs tied together) inverts the input square wave and applies it to the differentiating circuit R2-C2.