Column: Circuit drill
Assessing the performance of the frequency multiplier circuit
By Dr. Sulaiman Algharbi Alsayed, Managing Director, Smart PCB Solutions F
requency multiplier circuits generate output frequency that is a multiple of the input frequency. Tese circuits are found in many applcations, for clock generation,
frequency synthesis, instrumentation, consumer electronics and digital communication systems, among many others. Tey are very popular because they are reliable, flexible and easy to use. Tis type circuit is designed for
low-power operation, ideal for battery- powered applications and energy-efficient designs. Figure 1 shows a typical frequency
multiplier. Te value of the capacitor C2 is 0.01uF, but by changing it, the circuit can multiply the input frequency by different factors. Te higher the value of C2, the higher the multiplication. Some OEMs have augmented this
circuit with a programmable capacitance
chip, to digitally change the frequency multiplication factor – from 2 to 64 – allowing users to choose their desired multiplication ratio using external controls, making this circuit versatile and suitable for a wide range of electronic systems.
Experiment and results I set up this experiment to determine the behaviour of this circuit for different input signal frequencies. I used a function generator to feed an 1Vdc input signal into it. Te frequencies were then varied from 1-500kHz, in 1kHz steps. Te circuit was powered by 20Vdc DC,
and then the output signal frequency measured and logged at every input frequency increment. All circuit component values where
kept constant, to ensure that nothing else changed in the circuit except the input frequency. Te results of the experiment are shown
in Figure 2, where the x axis represents the input signal frequencies, and the y axis represents the output signal frequencies. From Figure 2, we can see that the output
signal frequency is double that of the input signal, with the multiplication factor being determined by the value of C2. Secondly, for all input frequencies of 129kHz and above, the circuit successfully delivered the output signal with frequency multiplied by the pre-set multiplication factor, which in our case is a factor of 2. However, when the input signal has a frequency lower than the threshold value (129kHz), the circuit delivers a completely different output. Tis zone is from 15-128kHz, when the output signal is multiplied by a factor of 20.9. And lastly, Figure 2 shows that if the
circuit receives an input signal below 15kHz, it will not deliver any substantial output signal. Tis was done to ensure consistency and reliability of the results,
Figure 1: A popular frequency multiplier circuit
08 July/August 2024
www.electronicsworld.co.uk
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