# Frequency doubling (electronics)

By the term **frequency doubling** are in the electronic non-linear circuits referred to, the output of the dual frequency having the input signal.

## Low frequency technology

The full-wave rectifier offers a possibility for signals with low frequency , as shown in the picture. After calculating the absolute value of a sinusoidal voltage of frequency f (above) with a full-wave rectifier, the pulsating DC voltage (very below) has twice the frequency. In addition, it has higher frequency components 4f, 6f, ...

## Digital technology

A simple frequency doubling of the square wave, which is common in digital technology as a clock, in the frequency range up to a few 100 MHz can be achieved with an exclusive-OR gate if one input is fed directly and the other with a slightly delayed signal (via RC element ). The resulting needle pulses are phase-bound and about as short as the time constant of the RC element. Since this method does not use a resonance filter, the input signal can have any duty cycle or be heavily frequency-modulated .

## High frequency technology

In high-frequency technology , stable frequencies are generated with crystal oscillators that can only be produced with relatively low frequencies. In order to be able to transmit and receive in the much higher VHF range, the generated frequency must be multiplied. To do this, you overdrive an amplifier in order to get a distorted signal. According to the laws of Fourier analysis, the more the resulting curve shape deviates from the sinusoidal shape, the stronger the harmonics . At the output of the amplifier, the desired double or triple frequency is filtered out by resonant circuits .

In microwave technology , for example, diodes or overdriven transistors are used in order to achieve frequency multiplication (also doubling) on their non-linear characteristics . The desired harmonic must then be filtered out by resonant circuits .

## PLL control

A phase-locked loop (PLL) has its own controllable oscillator, but this is set using a control structure based on a reference oscillator. A frequency divider in the feedback loop enables the reference clock to be multiplied, including doubling the frequency.

## Microwave technology

Extremely high frequencies in the GHz range can no longer be transmitted through wires like electrical currents, but only as electromagnetic waves, similar to light, only through waveguides . In order to generate harmonics, this wave must be distorted. All you have to do is install a diode across a waveguide and apply a suitable bias voltage from the outside in order to set the operating point on the characteristic curve. A mixture of fundamental and harmonics is created , from which the desired harmonic can be filtered out by means of suitably dimensioned cavity resonators .

The wave fed into the waveguide must be polarized with its electrical component parallel to the distorting component, at this point there must be a maximum of the electrical field component (phase matching).

## Analog in optics

In optics , frequency doubling is achieved according to the same basic principle: electromagnetic waves are sent through a *non-linear material* so that harmonics are created here as in an electronic circuit. Then the desired frequency component is extracted with optical filter methods and used.

## literature

- Ulrich Tietze, Christoph Schenk, Eberhard Gamm:
*Semiconductor circuit technology.*Springer, 12th edition, ibid. 2002, ISBN 3-540-42849-6 .