Frequency Multiplier Circuit

This frequency multiplier circuit can be used to convert any low frequency input into any desired higher frequency output.

There may be events when it is needed to measure a low frequencies using a high degree of resolution.

How the Circuit Works

The circuit shown here is intended as a frequency multiplier for just this purpose which uses a resolution of 0.1 Hz with a fast measuring time.

A block diagram of the frequency multiplier is displayed in figure 1. As can be found, this configuration holds more than a passing similarity to the (by now) relatively common PLL frequency synthesiser.

On the other hand, in this situation it is the division ratio which is fixed and not the input (or reference) frequency.

The VCO frequency is divided by 100 and then compared with the input frequency in a phase comparator.

The resulting phase difference produces a DC signal utilized to correct the VCO frequency.

Because of this the VCO output frequency will be precisely 100 times that of the input.

In the circuit diagram of figure 2, the input frequency is first amplified by IC1 before being fed to the phase locked loop, IC2.

The VCO output is divided by 100 by the two decade counters IC3 and IC4 whereupon its phase is compared with that of the input signal in the PLL itself.

The VCO output frequency is fed to the meter through the inverter made by N2.

Switch S1 is included in order that the overall frequency range of 30 Hz.. 10 kHz can be split into two independent ranges, 4.5 Vp-p, Power supply necessities are 7-18 V namely 30 Hz…300 Hz and 200 Hz…10 kHz. at around 30mA.

The input sensitivity of this frequency multiplier circuit is estimated as being around 25 mV, and the output voltage is around 4.5 Vp-p, Power supply requirements are nominal at around 7-18 V and 30mA.