Frequency doubler

This frequency doubler using a single 4069 hex inverter IC, a frequency doubler can be constructed to give an output pulse train whose frequency is twice that of a squarewave input signal. The signal is applied to the input of N1. It should be a squarewave with a duty-cycle of approximately 50% at level compatible with CMOS logic (3-15V peak to peak depending on supply voltage). The input signal is buffered and inverted by N1, and inverted again by N2, so the outputs A and B of N1 and N2 are squarewave signals 180° out of phase. The output of N1, is differentiated by C1 and R1 and the output of N2 is differentiated by C2 and R2, giving two spike waveforms of C and D, 180° out of phase. The signals are buffered, inverted and shaped by N3 and N4. These are then combined in a NOR gate consisting of D1, D2, R3 and N5, and finally inverted by N6 to give the frequency twice that of the input signal. The circuit will operate over a wide frequency range. With the component values shown the width of pulses in E and F point is about 500ns, so the duty cycle of the output will be 50% when the frequency is 1MHZ, when the input frequency is 500KHZ.By A.M. Bosschaert
Frequency doubler - schematic

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