I came across a frequency doubler circuit built with 555 timer IC. I checked this circuit with proteus simulation, but I did not get exactly double of the input signal frequency. I got this circuit diagram from the book Electronics projects volume 9 which is shown below.
In the circuit diagram, The reset pin, the trigger pin and the threshod pin are connected to the input. The value of capacitor C1 is supposed to be (25/Fin kHz)nF and C2 is ten times of C1, that is C2=10 x C1.
The following 555 Timer Frequency Doubler Circuit Simulation shows the input and the output signal when the input signal is a repetition pulses with 1KHz frequency and amplitude of 4V.
As per simulation I cannot say if the output pulses should have such small widths. There is certainly increase in the frequency of the output signal but the width should be like this I guess.