A frequency multiplier produces an output frequency that is a multiple of its input frequency, using non-linear signal transfer. It is used in communication circuits and FM systems. The heterostructural barrier varactor is a useful device for frequency multiplication.
A frequency multiplier is a device that produces an output with a frequency that is an odd or even multiple of its input frequency. For example, for a signal with a frequency of 100,000 cycles per second (cps) or 100 kilohertz (kHz), a frequency multiplier can produce a 200 or 300 kHz signal. The frequency multiplier is commonly used in communication circuits to produce the desired signal frequency given a reference frequency.
The primary mechanism for a frequency multiplier is called non-linear signal transfer. When the output of a frequency generator is viewed on a spectrum analyzer, there is a single vertical line with a high end aligned with the amplitude of the signal. The level can be 1 volt (V). The horizontal axis indicates the frequency of this signal. For example, the frequency of a 500 million hertz (Hz) or 500 megahertz (MHz) signal will be indicated on the horizontal axis of the spectrum analyzer.
When the reference frequency is fed into a nonlinear device such as a class C amplifier or diode detector, the result is a frequency spectrum with harmonics, or multiples, of the original frequency. By using a bandpass filter with the ability to pass only the desired outputs, the result is the desired harmonic. In the 500 MHz example above, a second harmonic can be derived at 1.000 MHz.
The frequency multiplier approach is used in special cases where only one output frequency is required, due to the various combinations of bandpass filters required to produce clean sine waves. For example, it may not be possible to directly generate a 10 billion cycles per second or 10 gigahertz (GHz) signal. It may be possible to use a 5GHz oscillator, or frequency generator, followed by a multiplier and bandpass filter tuned to 10GHz.
Also known as a mixer, the signal multiplier is used in frequency modulation (FM) systems to produce an FM carrier that is frequency shifted into the desired broadcast frequency. The mixer, unlike the frequency multiplier, requires two inputs. Although designated as an analog multiplier, the mixer output actually generates the sum and differences of the input signals.
The heterostructural barrier varactor (HBV) is a special back-to-back diode arrangement that has a capacitance that varies with the voltage across the diode. A single diode varactor uses a single diode with a capacitance that changes with the level of reverse bias on the diode. The capacitance peaks when the voltage is zero, while the capacitance decreases in the positive or negative swing of the voltage across the HBV. This feature makes HBV useful for frequency multiplication.
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